I'm gonna make another attempt to seal up the plug
tomorrow with a round plastic plate and an O-ring.
The O-ring will surround the drainplug indentation
and be RTV'd in place there. Then I'll RTV the round
plastic plate over that with heavy RTV outside the
O-ring. Hold it in place with a bottle jack and let
it cure. If that holds, I can use the fuel pump to
remove old fluid when it's changing time. I think
the RTV will allow flexing and expansion.

The plate is a wall-protector for doorknobs that tend
to strike the wall. I think this will work and save me
a lot of labor.