Leaderboard

Unless you remove the head, the drive plug comes up about a quarter-inch, more-or-less. The existing O-ring is junk. It'll be hard as a rock, brittle, and not sealing any more. But you can't get it out, and you can't put a new one in there. All you have left to do is to cut and wrap a gasket coated in sealer under the flange, Clamp it back down, and hope for the best. AFTER you get the head removed, the drive plug comes all the way out, and at that point you can break the old O-ring, stretch a new one back in, and theoretically that's all you need. The new O-ring is (supposedly) improved. When it was me, I put a new, uncut gasket in there for a "second" seal. https://www.amazon.com/Permatex-80007-Hardening-Gasket-Sealant/dp/B002YLVLY2/ref=sr_1_2?dchild=1&keywords=Permatex+%231&qid=1591581753&sr=8-2

BEST way to clean-out a gas tank is to haul it to a radiator shop, and let them "boil it out" in their radiator-cleaning tank. DO NOT blort a bunch of RTV under the flange of the oil pump drive. RTV that doesn't get squeezed between two clamped parts does nothing for sealing. Get a distributor gasket, cut a split in it, coat the gasket with sealer, (Permatex "hardening" sealer works for me) work the gasket into place. This will likely reduce the leak by 90+ percent, the only leakage would be at the split in the gasket. Even with the split, you might get lucky and have zero leakage. If you take the entire drive plug out, install a new O-ring...and the gasket for added protection. This thing exists because otherwise there'd be nothing to drive the oil pump; or it wouldn't be removable. this is all that remains of the distributor that the engine family was designed to have. Once the engine went to distributorless ignition, only the oil pump drive was needed. The only reason this thing is a pain in the ass is because you have to take the head off to remove it. If you could pull it out easily, a new O-ring every ten years would be no big deal.