AJS & Matchless Owners Club

Thanks Tony!
I don't think they sell Araldite here but there is a two part adhesive called JB Weld that would probably do the job. I think the mechanic wasn't thrilled about going that route, in case it breaks free and ends up in the workings inside the chaincase. I'll give it a try though.
Thanks again,
Dave

I think I'd take that risk rather than follow his previous advice to run the chain dry.

Yes, it did occur to me that there is that risk of it dropping into the primary chain. You'd just have to keep an eye on the screw for any sign of it loosening, (or renewed leaking).
JB Weld has a very good reputation.
Maybe you could have the nut silver soldered or brazed in place. The nut can be quite thin as it doesn't have to withstand much force.
It does seem a bit 'over the top' to replace the whole chaincase (if you can get a good one).
In desperation, and as a very last resort if the thought of losing the nut inside keeps you awake at night ( ) you could JB Weld a bolt on the inside and have a Nyloc (self-locking) type nut on the outside.

If you clean of the inside face to bare metal and de-grease it then JB weld is the way to go. My next door neighbour had nearly all his captive nuts work loose (no jokes please) and we JB'd them in place and 3 yrs later they're still good as the day it was done.