Just 1 rivet?
I have recently been fixing a bunch of tanks, but not looking for customers! A simple leak repair is fairly easy and un-intrusive, but while inside, aggravating factors may surface. I just did a single bay surgery on a -10 tank for a leaking vent line, but access would be similar for yours. if its leaking from the AFT baffle row, you likely have a fillet breach, if its leaking on a rib, its a fay surface/fastener breach. Hopefully, no need for a full strip and reseal. I'm currently doing a set of RV-4 tanks that has been full open, strip, de-slosh and re-seal..no bueno. Hopefully you can find a local sheet-metal savy builder that can help you (if your the builder thats you !). WNM is fantastic, but it may be bye bye to your paint job unless they match paint after repairs.