Old car woes... seat back clips, foggy projector headlight
 

After thirteen wonderful years, I'm really getting tired of brittle plastic and failed adhesives. I currently have three issues:

The hard back covers on my front comfort seats both have fallen off. The plastic clips come unglued, they don't break. Is there a recommended adhesive to put them back?

I have one headlight in which the low beam lens is very foggy (on the inside.) Is there a way to remove the whole headlight and clean it through the bulb opening? Cotton ball on a stick? Alcohol?

After 224,000 miles, the front bumper has been off a few times for various timing belt, water pump, etc. repairs. Now the passenger side seems to be about two or three millimeters lower than the driver's side. Yeah, I know, big deal, but it bothers me. Seems like the clip on the passenger side next to the front wheel just isn't holding it up securely. Is there anything to be done about that?

Probably try epoxy glue for the seat backs, epoxy is really strong.
I had the same bumper issue and i actually glued the bumper studs holding the bracket onto the body since they were old and brittle, used epoxy as well and has been holding up well.https://www.audiworld.com/tech/ext46.shtml have a look and see if that helps you.

Cool, that makes sense for the bumper. I'll try that. I used a cyanoacrylate adhesive and clamped the clip for 24 hours, so far so good.