Hi N1KK0,
Drill through the old weld and weld back through the hole, not easy and depends on your welding ability. You may even have to lengthen the stub before you can get enough surface to weld to. Bit fiddley but can be done, both arms have to be on the same angle. Sorry I can't see what the cause of the rear axle droop is but it must be obvious, the axle is a solid piece side to side so it is either a problem with that or the base or bush is worn
