1996 Bonneville: just opened the gas cap door, and heard the top half of the little closing spring break- darn! Problem is that the spring is retained to the door by a flat peice and some spot welds. Is there any fix out there for this one?

Not that I know of. My 97 gas door is on its last spring too.

I know you can get the spring, it is GM part number 12503691, I am not sure how you replace it though.

Can you post a picture?

OK, now I'm worried- if you veterans here don't know a solution, I'm in trouble! Looks to me like the door is attached to the body with threaded posts welded to the hinge- I assume fasteners (nuts) are on the inside, and that you have to replace the door as an assembly. I'm confused that the spring is available separately, obviously I'm missing something.

I see now, duh. From the looks of it in your pic, your going to have to find a way to apart the crimp to remove the spring and the new just goes back into its place and the arms just pop into the holes. Then re-crimp with vice-grips or something.

I removed the spring from a parts car by bending the little tab that holds the spring and putting it in my car. I did not have much luck. The metal is not resilient enough to bend open and then bend it back, it is to brittle. I found that the lock will hold the door closed when the doors are locked. I simply push the fuel filler door closed after I lock the doors. Been doing this for at least 6 years. It becomes force of habit.

Trying to think outside of the box for a fix..

I'd try to get a new spring, and cut the spring in the dead center where it goes into the fuel door, then put the spring on and get something like a small sewing needle, and stick that in to help support the break you made, and keep it from moving,maybe put a dab of JB Weld on the top and bottom of the are you would normally crimp shut.
I think that may keep the spring from popping out of the crimped area on the fuel filler door.

If that does not make sense I'll try ti work on a pic to give you a better idea of how I am suggesting to "MacGyver" it.
Even if it does not work, you wont spend but a few bucks for the new spring, and it can't hurt anything to try what I am suggesting.

NOTE: To remove the old spring just use some tin snips and cut it above where it enters the crimped area.

This car doesn't have a locking fuel door. But I appreciate the comment about the spring replacement experience not really working. I will buy a new spring first for sure, and see what others come up with for advice on how to actually install it. Too bad it'* location is so risky, otherwise I'd have cut open the crimped retaining part of the hinge, and mig welded the new spring closed at the crimp. Just two short taps of filler metal yo hold it...but the possibility of fumes-BOOM!

A quick eBay search shows a few salvage sellers offering fuel filler doors- only as an unbolted assembly. Seems like that my be an option- buying one and painting it might be a better option than messing with a replacement spring. Although, if I can get a new spring, I could weld it into the pinched/crimped hinge to hold it. Would remove the door from the quarter panel (first remove the black plastic shroud around the gas cap), then deal with the spring. Just a thought...