FWIW:
From what gridleak is reporting, & possibly suspecting, one can confirm & read in the 1975 Volume 2 of:
"How To Restore Your Model A", (from The Restorer), page 21, TINT TIPS .. FROM READERS:
where one gentleman reader prepared & tested a gas tank sealer consisting of 80% Permatex mixed with 20% of eighty proof alcohol to coat his gas tank "after" rendering a positive sublimation test in the then gasoline "without" ethanol.
Have no idea how many Model A owners followed these instructions to seal their gas tanks with this prescribed sealer; however, it appears my tank had this sealer until the previous owner began using ethanol gasoline ........ then this sealer began to dissolve & had black tar like chips in the bottom of the gas tank mixed with rust flakes.
On the first short test run after engine overhaul, witnessed soft tar-like material in the carburetor & intake manifold -- carburetor cleaner removed some, but witnessed POR 15 Marine Clean dissolved it instantly.
Could only drive about 1/2 mile before having to disconnect gas line at carburetor & blowing in the gas line to unclog the shut-off valve on the bottom of the gas tank.
After cleaning carburetor & intake with MC, cleaned gas tank with warm water & POR 15 Marine Clean circulating & forced through an electric water pump -- not a problem since this last cleaning.
Hope this helps.