I bought my car about a month ago, one of the first things I found while doing my inspection was a good nick in the paint at the edge of the gas cap door and that the locking peg for the door wasn't moving at all.

After I dig through the manual, I found that the peg has a pull string, and looked to be held in by a clip to the actuator/solenoid thingy. The only thing was, the picture in my manual showed a car with no sub, and I couldn't believe that the huge box pictured was just to move that peg. So, I disassembled the trunk, and found out that the actuator/motor was moving just fine, but the peg wasn't connected to it, what's more, it looked nothing like what's in my manual. So, I ordered a new actuator (because the peg, actuator and connecting plastic piece that I needed are only available as a whole unit. The red pull tab is not included with it though. After getting the part in, it's easy to figure out what happened: Either a gas thief or unwitting person pried open the gas door with it locked, and instead of the peg bending, the plastic piece broke. It's advisable not to pry the door open or slam it shut as I can see this piece breaking easily.

Time for the project: about 2-2.5 hours realistically, ideally it would take about 45 minutes to an hour, I'll explain below.
The actuator part number is: 4B0-862-153
My dealer charged $73 for it, so most dealers will probably charge 25 cents, I mean 60 something. (is it just me, or does it seem like that P/N is missing 3 digits? that's on the box and the invoice, oh well)

Before you start, I recommend that you fold the back seats down (in case you "accidentally" get locked into your own trunk, or if you want to entirely remove the side panel in the trunk).
You'll need a philips head screwdriver (medium-large, but not those useless huge ones), a long 8mm socket with ratchet and extension (unless you want to use a wrench and fight with bolts), and either a putty knife (plastic), a thin graphite rod, or a flat head screwdriver (something to help pry the rubber seals ont the outside of the plastic trim on reassembly)

The first thing I did, was to open the trunk, remove all the junk, cargo net, passenger side panel opening thing, and trunk floor:





You don't have to remove the trunk floor, but if you don't. you'll constantly be shifting it around as you remove panels and stuff, I do put it back in later.

After that, you can start removing things.
the first things to remove are the 2 cargo net loops on the rear plastic trim, and optionally, the cargo net loop all the way in the trunk (it makes your life easier and is needed if you want to completely remove the trunk side panel)
Simply pull the loop out, and it'll expose the 2 screws that hold it in place, they are quite long on the loops near the back seats, but not too long at the back of the trunk.



Once the loops are removed, you need to remove the rear plastic trunk trim, it's held in by 2 screws just above and toward the center of the car from the loops. remove the screws and pull it up at about a 45 degree angle to snap it loose. you can pull up only, or out only, but you may break it pulling straight out(there's some plastic hooks in the middle), and pulling straight up is harder as well. once popped loose, I removed the light and left it dangling in the trunk.(this is the most frustrating trim piece to put back on I've ever encountered, have soothing music, a nice glass of wine (or beer), or other stress reliever handy for putting it back on, it takes me about 30 minutes after doing it a couple times)

Next, there are 2 hooks/clips at the bottom of the opening in the side panel, just below the sub, I used a large pocket knife (it was handy) to pry them straight up, but a screwdriver or metal putty knife would be safer and work just as well.

Then, there are 2 plug style clips that you'll need to remove. these are plastic, and break easily if bent, and they are 2 pieces, the picture below shows where they are.


A closer shot of one of them removed.



Now, pull the upper real plastic trim piece toward the middle of the car, it should pop out, still attached to the side panel, it's held on by 3 metal clips. (this is the 2nd most frustrating piece to put back on)

At this point, you can do other stuff to remove the entire side (not needed for this job, and a big PITA because you have to remove the side of the rear seat, and maybe loosen the hat shelf), or put the floor back into the trunk to give you a nice working surface. if you do put the floor back in, push it as far to the drivers side as it will allow, ensuring that the lowe lip of the passenger side panel is exposed, so you can slide it over the floor. I had to turn up the flexible portion of the drivers side of the floor in order to get enough room.
The side panel is surprisingly stiff, but still flexible enough that you don't have to completely remove it, and it seems like it has some type of adhesive applied to the top and bottom of it to hold it in place well. I just pull it in a bit so everything is exposed.

The sub is held in by 3 8mm bolts, one is really easy to get to, one is really tough if not using a ratchet, and the farthest one forward of the car is just awkward. the picture below shows their locations.



I used a long thin 8mm socket with a 4" extension on a 1/4" ratchet to take these bolts out, which made it pretty easy, though a slightly longer extension would have made it stupidly easy.



With the bolts out, you don't need to unplug the sub; the wires are long enough to just move it out of the way.
Congratulations! you now have access to remove the actuator!
it's held in by 2 screws; you just need to loosen them, slide the unit forward so the heads go through the large portion of the keyhole openings, and pull it out.



To unhook the wire, simply press the 2 pieces sticking out of the back of the connector toward each other and pull it out.

If the peg isn't out yet (you didn't get it out already, or it didn't come out with the actuator), reach around and pull it out.
here's my old one, just above my new one:



Remember to move the red pull line over to the new one and make sure it's going to where you can reach it when you mount the new actuator.
before you put the new one in, open the gas cap door, so that you can test things out and see everything working before you put everything back.
when putting the new unit in, the connector goes down, make sure you plug it back up, and I gently guided it through the rubber grommet to the door opening before trying to line it up with the screw holes (though I used it them to eye about where the grommet is)

Now, after getting the actuator in place and tightening down it's mounting screws, walk around, make sure you can still see the tip of the peg through the grommet and test things out by locking and unlocking your doors a few times, make sure it works with the door open, then with the door closed. mine still had some play with it locked, but it's better than it being unlocked all the time.

If everything is fine, put everything back in reverse order, keeping in mind the notes below. if everything is not fine, check connections, adjust any alignment of the grommet, cheek the loop on the door, and is things still aren't right, you have some other problem.

Reassembly notes:

-When re-mounting the sub, it's best to start all 3 bolts before tightening them down, the plastic enclosure is flexible, and if the holes aren't all lined up just right before tightening any of the bolts down, you'll have to really stress the plastics to get it lined up, or end up loosening them anyway.
-When putting the 2 plastic plugs back into the holes in the side trim, take the 2 pieces apart and put the lower part in first, it will go in easier, and you'll better be able to make sure it goes in all the way.
-When putting on the rear plastic trim, get the 4 metal clips lined up with their holes so that they go straight through the middle (you'll have to put it up to the back and adjust by feel), and make sure that the hooks in the middle will go to their appropriate spot. it's also best to get things lined up, get as much all the way on as possible (usually I do one side all the way in, then the other), then pull the rubber gasket up on top of the plastic trim, I usually start at the end and work in, I do one side, then the other, and do it again when done. I also use an old thin graphite shaft that was used in an old kite, it works great, but a plastic putty knife will work just as well, a flat head screw driver will work, but may scratch stuff up.
-Remember that you WILL need something soothing/relaxing near by when doing that rear plastic trim (I really despise it)