Thicker seal isn't the problem it's the lock ring. The lock ring is to thin and bends.
And, when you figure that out then use a factory ring let's hope you've bought a good tank and it doesn't bent the tabs on the "new" tank...
I remember on one occasion going out for a build's maiden voyage pulling over for a quick inspection and seeing a drip at the sending unit...I crawled under there and just touched the sending unit and the lock ring popped loose from it's position !!! Talk about panic strength to reseat the whole mess along the road...I figured I was going to be a roast toasty when the gas hit the hot exhaust... That's the last time I've used the cheapy lock ring on anything...
