The right fuel tank cap flange is not my friend. This same rivet continues to leak. I’ve inspected with mirrors, flashlights, magnifying glass, and fingertips to no avail. It drips the third test just as it has the first two. At this point, it was clear that there was a path for the water to get to that hole from somewhere obscure and slathering proseal on the back isn’t fixing it. I decided to drill it out all together.

I then surgically removed a chunk of proseal from the back of the flange covering the shop head. I cleaned the area well and mixed up a mini-batch of proseal, this time resealing the hole from the front before inserting and setting the rivet. I then resealed the back and put one more generous layer of proseal, basically covering the inside of the skin and flange from the end rib all the way over to the flange.
The good news is that the once-large leak is no more and the rest of the tank was finally behaving. All of this testing time has given me ample opportunity to finish up the leading edges with a bit of help from the Mrs. and a buddy who came over to drink a beer and was voluntold to learn how to rivet in quick order. He now owns 1/100,000,000 of an RV-10!