Don't use Randolph again. Ever. Use PRC 1005L Buna-N, available from Spruce.
The sealant is diluted in MEK, you pour, slosh, drain excess, let dry
and
you're done, and its impervious to any fuel additives.

I seem to remember the Randolph site says that 912 is no longer
available. I also can't find on the 'Spruce site where PRC 1005L Buna-N
is at all alcohol resistant.
That said, has anyone tried that POR-15 stuff? Or the 'alcohol
resistant' sealer on Hirsch Auto's site? I'm looking since my RV tanks
are over 16 years old and starting to seep.

Jim