There was a thread a few months back about this issue and apparently Mazda released a new gas cap following the 2008 model year; said new cap IS on my early production 2009 Mazda3 and can be idenified by looking at the locking lugs on the cap neck. Apparently the old locking lugs were an open three sided "C" style lug, and if you happened to fit the cap so that the open end of the "C" grabbed the lug in the filler neck, it would jam. The new cap has a closed lug, a "D" style if you will, that looks more like a parallelogram.

The above said, even though I know that I have a new style cap, I make very sure that when I put the cap in the filler neck, I push it in so that the top of the filler neck and the base of the "hat" of the cap are making complete contact before I turn the cap to lock in in place. So far at least, I've gone just over a year and 22,000 miles with no stuck cap. Is it the new style cap or is it the way I put it back on that has been successful? I don't know, but I'm sure as heck not going to be experimenting to see if I can get it stuck.

 

A picture of either would be awesome!

 

I'll see what I can do about that tonight.