Anybody know of a vendor selling a new or used rear differential mount, the mount at the front of the differential by the prop shaft?

I see a few in the $250 range but don't want to spend that much.

Also, I've read that a few people have used window glass sealant to repair old mounts. Anyone done this?

 

I recommend you hit up a junkyard. Some junkyards let you go and get what you need, some ask what you need and they get it for you. Either way it will be cheaper than retail.