Sounds like my header tank (and many others) I fight battles with fuel smell
constantly, I have pretty much concluded that the header is simply porous
enough that fuel migrates right through it. I don't get stains (I run 100LL)
I don't get drips, but I always have odor. Year after year I go through
it at annual and occasionally find a weepy fitting (you guessed it) at the
header which I fix (again). I think the only real solution is to scrap the
plastic header and go to the aluminum one.
Regards,
Jeff Hays
Series 5, IO-240B