Hi, i have been keeping track of this topic, as i need to fit a new boot and, in a distant future, i need to fit the door as well after my car has been repainted.
Lots of people were fighting with it, so I started to look at the parts and how they are attached. Now's the time because my boot floor is out and i will never have more convenient acces then now.
Just to tease, here is a modification that will make your life so much easier:
With this bit of aluminium cut out, you will be able to install the gas flap one handed, without a need to (partly) compress the spring. You can almost throw it in.
The removal of the gas flap (gas door) is needed to replace the rubber.
And the removal of the door is difficult, because of the spring loaded hinge.
Removing the gasflap without some experience gives you a good chance to scratch your paint. Re installation after a full paint job makes this assembly job even more stressful.
Here is the inside view without the rubber, to show you how it looks like in there:
Now i do not have a solution to get your gas flap dismounted without sctaches.
But with the above modification, it will make it effortless to reinstall and deinstall it (if ever needed again). I now can do it one handed. No scratches....
The thing with the gas flap is that it is held with three (M5) nuts, which is akward, as there are only two access holes from the trunk through the rubber. Especially the middle nut ( the one towards the front of the car) is difficult to unscrew; you have to angle a socket up or down through one of the 2 acccess holes to unscrew that one.
Once the three nuts are off, then the next step is to remove the flap. I found that the best way ( actually from advice in previous posts in this thread) is to take a flat screwdriver into your trunk, and stick it between the local glued-in reinforcement on the quarter panel and the rubber. Aim for the middle bolt, that one is keeping the door from falling into your hands. With the flat screwdriver, gently pry the gas door mounting plate away from the fender. The mounting plate should move to the middle of the car, and just pop off the middle m5 stud. Now you can, with the door in the fully open position, slide the door towards the rear of the car. It will travel about 25 mm, an inch. When the hinge inside starts touching the rubber edge gently rotate the door to a half closed position. Don't operate the hinge, just rotate the assembly. Now the fueldoor can move another 15 mm to the rear, and the door is free.
The screwdriver thing above is what makes it almost impossible to get it back on without high forces involved.
Now that you have the fuel door in your hand, get something that eats aluminium/um, a dremel or air spindle works just fine.
Now chop out a good 75% of the material thickness of the mounting flange, just next to the middle hole. As such:
This extra bit of space actually allows you now to get the mounting plate to just clear the top of the middle bolt when assembling or disassembling this thing. No scratches ever again!
Here's video of me trying to show you all how easy it is afterwards; mind you it is done one handed!
In this pic you can just see how the middle bolt prevents the fuel door from sliding over the bolt. If I had enough guts, or a spare door, then I would have completely removed all material (following the blue dotted lines), allowing the mounting plate to simply slide in; even better. I am not sure however that enough rigidity remains if you create a full slotted hole.
I do not have a second door, so I can't test that ...
In the pic below, you can see just how the flap and the M5 studs line up. Notice also the reinforcement plate that holds the three bolts; it is spot welded on the edge of the door opening only, and thus it bends easily. (When you walk into and bend your gas door at the gas station , as mentioned in previous posts, I think this reinforcement gets bent)
I think this is the one part in the car where you can see that bmw also employed apprentices in their engineering teams...