I have new caps on the way, but just wanted to insure all else is ok. I fill the tanks with warm fuel to the brim. The next day, it is still to the brim, no vent leaks, etc. Go fly and upon return, one tank cover has a bit of blue dye weaping out. Is this just the cap? The caps do have some resistance when locking down, but on the advice of a friend who is unaware of this "weaping" cap suggested that I get the "good" caps from Webco. So I did. All fuel gauges, etc are normal, so am I correct in blaming the cap?

Thanks

Probably the caps. Soaking the rubber in MEK will soften the rubber a couple of times, but eventually it gets too hard to seal correctly. Other possibility is there is usually some fuel spilled in the fuel door area. If you fly before this has dried it will suck out around the door (not necessarily the caps) and stain the wing. Have also seen this happen with dried fuel in the door area after a rain, where small amounts of moisture liquidate the stain and allow it to stain the wing

First try tightening the cap. If that does not work give it a soak in lacquer thinner or acetone, Stay away from MEK, it will cause the cap to loose elasticity over time and is really nasty stuff health wise.