What's that smell?

Last weekend when I opened the garage door I was hit with the beautiful smell of gasoline. After the initial pleasure of the aroma subsided, a more serious thought entered my head:

"Why does the garage smell like gas?"

Of course my first suspect is the CL. I take a look under the tarp and sure enough, there is a spot under the center stand that smells of fuel. Only a stain remains, but there was definitely some sort of leaking going on.

I'm surprised by this because I tested the tank repeatedly after lining it and found no leaks. I even replaced the petcock with a NOS one, and it has been turned off ever since I parked the bike for the winter.

I took a close look at the lines, the carbs and anywhere else that fuel flows and found nothing. Of course the liquid fuel evaporated before I became aware of the leak, but I was hoping to find some tell-tale residue or something along those lines. Nothing.

So I moved the bike to a more level spot and kept an eye on it. Everything seemed fine for a few days, then one morning, another spot.

Now when this happens, it's not a lot of fuel, the spot is only about a foot around and there is plenty of fuel left in the tank. My only guess is that it has something to do with the +-30 degree temperature swings we're experiencing around here lately but I still can't find the source and I'd like to address this before the snow flies and I go a week or more without opening the door.