I suggest taking it to a welder, for patch up welding. Should be only $50 or so. Even a bit of weld on surface without grinding would be stronger than collars. Do it quickly to keep heat down. I've stick welded cracked hydraulic cylinders with oil in them using 6010 for first pass. Looks like chicken poop, but it seals it, then grind and 7018, if you like (ports have to be open on cylinders). If one option is to get new rear end why not try welding first.