Reinstallation
I just did this last weekend. It took about 20 minutes to get it all sorted.
Step #1 - Install rubber boot around body flange. The three studs should be poking through the 3 holes in the rubber. Remove the two rubber plugs.
Step #2 - Wrap the gas flap panel with a dish towel and tape. Some additional tape around the filler opening is probably a good idea.
Step #3 - With the door spring in the "open" position you should be able to slip the flange/spring assembly around the body of the opening. At this point the forward tip of the mounting flange will bump up against the forward stud. Using a screwdriver with the tip of it's blade bent at 90°, from the trunk side, poke it through one of the two holes in the rubber boot. Slip it under the front lip of the flange and then pull towards the interior at the same time as pushing it forward, thereby slipping the flange hole over the forward stud. The flange should be over all three studs now.
Step #4 - Thread a nut on the forward stud as far as possible. You should be able to reach through the opening to do this. The two rear studs will not stick out through the flange holes far enough to get a nut on.
Step #5 - carefully close the flap door. It will not close all the way because of the towel. This should now have exposed enough of the rear stud threads to get the nuts on. Working through the two holes in the rubber boot (a flashlight inside the boot will help) and some putty (per John's suggestion) place the nuts on the two studs and carefully tighten them. Make sure they are not cross threading. Work all three nuts evenly.
I do agree that this is not one of the more pleasant CS tasks. I did have an advantage because the fuel tank is out of the car, so I could sit inside the trunk space on a stool comfortably facing the rubber boot.
Thanks Sven and John for the instructions for replacing the gas filler door.
I started out doing this without searching for this page on the forum. Needless to say I wasted a bunch of time and had to start over. What a PIA job.
I did discover a tip that might help others.
After constructing a handle to pull up on the edge of the mounting flange I still had a very difficult time trying to pull up and push forward on the door to get the back edge over the first bolt.
Those springs on that hinge are quite strong.
So I was sitting at my desk/workbench and had some bolts sitting there for the beltline trim and was able to wedge one in the hinge and tilt the hinge just enough that I could put it up next to the bolt and only have to pull a little to pop it over the top of the bolt. Success! See photo.
I didn't have any body putty so a little upholstery headliner glue was handy and made the end of my finger very sticky to get the washers and nuts on.
BTW you can put 2 nuts in the end of the 8mm socket to bring one out to the front of the socket so you can get it started on the bolts.
So glad that is over with.