Drilled drain plug and filled unit with some Amsoil 80W90 Severe Gear oil:

Service manual calls for 1.22 qts (39 ozs), so had to use a little from a second one.

Drilled (technically drill size “R”, but closest fractional size is 21/64″) then tapped for 1/8-27 NPT:

I was gonna go with the magnetic NPT drain plug, but I don’t like the idea of constantly breaking the seal of an NPT fitting doing maintenance.  Decided on an NPT to Flare fitting adapter:

Now I’ll never have to break that NPT seal.  Just undo the cap:

Cap is on tight with an o-ring seal, but just in case, for double protection, here is some adhesive heat shrink to keep it from spinning off over time (that would be catastrophic).  It’s easy enough to cut with a razor and peel off when time to do the service: