S-Tronic oil leak at the back
 

Hi, I'm new here ;)

I just did full service to my car (60k miles) and I've noticed a leak at the back of a gearbox. Maybe someone can help me to find out what happened. Gearbox oil changed at 40k miles at Audi Hull UK.

Do I have to take out whole gearbox or just the back part?
What could be the cost to fix it?
Do I have to change gearbox oil again?

Pics:
https://1drv.ms/f/s!AlgMwVXUKv71gaZEtOVDH4j6CZ8wrQ

Thanks

Clean it and see if it "sweats" out again.

Not much of a leak, more like a "seep", or maybe left over from refill like porksoda suggests. If drops are not hitting the driveway, you can probably go another 60k like that without issue.

+1!

That looks like a DL501/0B5 S tronic transmission, which surprised me. As an aside, that engine is right at the torque limit for the transmission. Whilst the C7 S6 is also rated at 580Nm, your TDI is making the same torque at much lower rpm, which is more stressful for the transmission. Which is why the next iteration of the 3.0TDI with 600Nm moved to the ZF8HP based Tiptronic.

There are two lubrication systems in that transmission, an ATF system for the Mechatronics unit, and a gear oil (MTF) system for everything else, including the centre differential which is what is in the centre of your photos. The MRF contains a special additive for the centre differential, IIRC.

The traces of (gear) oil are at the connection of the centre diff housing and the main transmission housing, which will be a gasket, not a replaceable seal.

Only the ATF fluid is changed as a service item, the gear oil is a lifetime item. So this has nothing to do with your 40k mile ATF fluid change at the Hull dealer. You would need to remove the transmission if you wanted to replace the gasket. You could check the torque on the lower bolts. Whilst it is a lifetime item, there are both a filler/ inspection plug (almost visible in your second photo) and a drain plug for the gear oil. Which means your dealer should be able to ascertain the gear oil level, and top it up if required. Not something for you to attempt unless you have a full service manual and the ability to determine the gear oil temperature.

I agree with the other posters, this looks very slight, and is likely from vapour rather than oil dripping out. Many vehicles probably have similar traces of oil vapour deposits, but yours is amazingly clean for a 60k mile vehicle which makes it appear worse than it may be. Get the level checked if you are concerned.

Some reading, although most articles are concerned solely with the ATF change, you will see the relevant parts:

DL501 0B5 S tronic
0B5 DSG, S-tronic, 7-speed 35000 mile service, fluid and filter B8 A4, A4, A5,

Thank you very much for all info. First I'm gonna clean it and check again after some time.

If I decide to take the gearbox out and change the gasket what price you think I can expect?

thanks for the info

i have a similar "sweat" on my C7 3.0T at that area. very minor IMO considering that I have almost 100k miles. Not planning to do anything with it, since it is very very minor and not worth the hassle as long as it doesnt get worst before the sell the car in a year or 2

I was looking into how to change the gear oil (not the ATF fluid) but from what you are telling me that's not needed. What about the rear diff? does that needs to be serviced at 100k?

thanks

I'm worried that the oil might be dropping on the exhaust pipe as you can see on the pic the dark spot on it like its burned while driving so maybe its not only vapour.
also I see some marks in the carpark where I usually park but hopefully it's not mine. We will see when I clean it.

Sorry, don't know what sort of price would be charged, never had an issue with either of the two cars I had with the same transmission. What I would do, if concerned, is ask the dealership to check the gear oil level, which should not be expensive, and top up if necessary. If it does need to be topped up, the amount would give you an idea of how significant, or not, any oil loss is. I think, as per Vodka G's post, that some sort of small scale seepage around this area is quite typical.

Replacing the gear oil is certainly not on any Audi maintenance schedule. But plenty have done so, possibly this was preventative maintenance when the transmission was being highly stressed (very high output S6 modifications, way over the recommended torque ceiling, etc). Or perfectionists who argue (probably rightly) that there is no such thing as a lifetime fluid. I suspect changing the gear oil is a simpler process than the ATF, and there is no filter on the gear oil side. It is very rare to hear of gear set / drive shafts issues with the DL501, it is usually the Mechatronics side that has an issue. But I thought North American C7 A6/A7 with the 3.0TFSI were fitted with the ZF8HP - maybe this happened later in the model life?

Not sure if you are referring to the Sport differential, as they are the only ones I've used for the last decade or so. I have read anecdotally in forums that it is 100k miles, but I have never got close to that so don't know personally. I was never convinced the 100k miles figure was an actual Audi service requirement, though. As the centre diff uses the DL501's gear oil, and that is lifetime rated, I believe Audi also regard the rear differential oil as lifetime rated. Audi require only the ATF and lower filter in the front section of the DL501 to involve a service interval.