I put some liquid silicone gasket on the tank side- I'll post what happens
I am 100% sure that was a bad idea.
Here is what I did.
The gasket on the cap is donut shaped.
Take the gasket off of the cap
Make a donut shaped gasket shim out of some 1/32" gasket material
Put the shim inside the OEM gasket
Put the gasket back on with the new shim inside. This will take some patience.
It may be a little stiff to close but it will get better with some time.
I did this 6 years ago and it solved the problem.
Search "gas Cap" you'll find some reading
http://www.valkyrieforum.com/bbs/index.php/topic,5881.0.html