[twobjshelbys]

Comparing apples and oranges, I think, but possible hints. Bob, can you post a pic of the inside of your filler cap?

PatrickT has what looks like a traditional fuel filler neck inside the quick fill surround. In this case though the filler is recessed so overflow can sit in the ring around the quick fill.

Bob's on the other hand sits on the surface. So... If the construction is similar, gas expanding and getting past the gasket on the traditional fuel cap has a nice little place to puddle and seep past any pinhole that is in the sealant around the filler tube where it meets the quick fill cap. With the seal of the big cap, any gas sitting in that area can't evaporate, it'll just puddle and if there is a pinhole in the secondary sealing just keep looking for a way out.

I seem to recall that on my CSX the quick fill was "live" - the top had a gasket that sealed. It had a pretty good funnel-shape that would probably have held a good amount of expansion and any spillage would have been over the top of the cap. In Bob's case it looks like it came from around the bottom of the LeMans cap area and then found a way under the paint...