This is annoying. When we re-painted the gas tank on my 250 Husky (about a year ago) and took it out in the spring, we found that the gas cap magically stopped working. It just refused to be screwed onto the tank firmly and leaked gas all over the new paint. Annoyingly, even though we used brake caliper paint which is supposed to stand up to insane heat and brake fluid abuses, the gas was just starting to eat away at it. Balls! Our solution was to just fill it up 2/3 and ride easy, and then put a new cap on after the ride. We got the new cap - a high-end piece crafted out of a solid chunk of billet aluminum, and it worked perfectly.
Fast-forward to a week ago. I go into the garage to check on (stare at) the bike a bit, and get the idea that I might as well check to see how much gas was in the tank after the last ride, which was almost 4 months ago. I take the cap off, note that it's about an inch from capacity, and go to put the cap back on. It turns about 15 degrees and stops. More pressure. Nothing. Being the engineering type, I take a moment to examine the cap and the tank to see how it's supposed to work. Satisfied with myself (and a lot of unavoidable pre-mix fumes) I remove the gasket to see if the cap will fit without it. It slides on without problem, but the "slosh test" reveals that it leaks in this configuration. I put the gasket back on, pry the cap on as far as it'll go, and do another slosh test. More leaking. It seems to me that the gasket is too small somehow. It looks like the inside diameter is small enough that it likes to "ride up" on the cap and not go down all the way, which doesn't leave enough clearance to screw the cap onto the tank. That's my guess, anyway.
What should I do?