[bobkatfly]

So, after over-thinking this (sorry Dave), I decided on the following plan.
The threads in the housing are about 3/4" long.
The threads on the plug are about 3/16" long (3 threads on a 3/8-16 thread). A little skimpy in aluminum. I believe that lead to the problem in the first place.
I was going to go with the Time-sert but was worried about drilling a straight hole with the drive installed. If the housing had been removed it would have been a different story. Also, the Time-sert kit is $80 plus additional cost for stainless inserts.
What I've done is modify a 3/8 bolt with about 1/2" thread length and machine a neck and counterbore under the head similar to the original, then drill the end and shrink fit the magnet in. I was lucky enough to re-connect with an old machinist friend that did it for a nice dinner that I didn't even have to cook.
Attached are pics. You can see the old plug with magnet removed, a new plug that I bought and the new screw with the o-ring installed.
I'll be trying it out soon.