You can try a pure silicone grease on them, I've used Parker Lube in the past but don't believe it is rated for fuel
If you can find an industrial source for sheet rubber, they may be able to cut some square ones for you some if they are a funny
size. They may stock nitrile, viton, or silicone rubber o-rings in the size you need. You may have to find someone with an account with them.
If you are trying to use hardware
store variety, they are probably not be rated for fuel
, swelling up then cracking and falling apart. NAPA or another parts
house would be a better bet.
Good luck with it!