I had the same exact issue on my 8a on the left wing. Proseal along the bottom seam was soft and wiped off with an acetone rag.
Once I realized how easy the tank removal and reinstall was (except those darn brackets to the shear web!) I decided to forego major surgery on the tank and simply removed ALL Proseal external to the tank, thoroughly prepped with scotchgard, Wiped down with MEK, then reapplied fresh, thoroughly mixed cartridge of proseal. External only.
I have 50 hours on it since the repair and have been watching closely for leaks. After 10 hours, I pulled the root covers, and all was dry. After 40 hours I pulled the inspection covers and it looks good. So I’ll keep an eye on it and check every conditional, but so far I’m happy.
2020 - RV8a N81081
Bubba "At Large"