Jonathon,

What I did was get the correct size and thread pitch fake Helicoil.  This
cost about $70 with the drill.  A real Helicoil was about $25 more.
 However, the size is the same as for a spark plug, but the pitch isn't.
 So, what I would do next time is use a spark plug fake helicoil kit for
about $25 (including drill) and modify an old spark plug into a new drain
plug.

I found that with the narrow shoulder on the drain plug (or spark plug for
that matter) a soft gasket was a good plan.  I first used aluminum, but I
found that I sometimes had to go back and re-tighten the drain plug, so I
switched to throw away cardboard gaskets.

Another solution is a rubber expanding plug for about $5.  These probably
don't last forever, but also probably don't fail slowly, so when they start
to leak, you just spend another $5.  I didn't go this route because I saw
the plug as the lowest part of the engine and thus likely to scrape on
something.  But in reading this list, I've never heard a person complain
that they used the rubber plug and had it scrape off.

Either solution should be available at FLAPS.

Mike   '84 GL   '58 Isetta