Here's a
LINK
The other thing you might try is to get one of those aftermarket plugs from SOR and others with the allen head. They're longer than stock and will sometimes be able to grab the lower threads if they're still good.
I bought the tool that was used in the above link. (expensive) Heli coil wouldn't work because there is not enough material for it to bite into. The wall of the case is very thin at that point.
In the above link, if you send him your split housing, he'll do the repair for $30 or so...
And I wouldn't do it with the t'case still attached.