Me too. I looked hard at my worst tightest filler neck and it looked like the mold was worn. The threads at split don’t match well. Maybe just poor QA, but also, guessing maybe it’s made from a filled nylon, IDK. In addition to the high coefficient of thermal expansion typical of plastics, nylon absorbs water like crazy, making dimensional precision impossible in a wet part.

And of course cranking on the cap is rough on the hoses.

I found one at a boneyard that isn’t so tight. But I REALLY like the metal one. Might give that a try.