Cracked rear driveshaft slip yoke: weld or replace?
 

The characteristic "clunk" going in and out of gear lead me to check out my rear driveshaft and sure enough the front ujoint behind the transmission totally failed. Dropped the driveshaft, got the rental tool and went to work removing the old ujoint. I'm not sure if I was just too rough while removing the ujoint or if the yoke was cracked to begin with, but either way, the yoke is cracked at the very top of one of the driveshaft ears. Obviously I don't want to reinstall the new ujoint and throw the car back together as is. Question is, is the crack (it goes all the way through the ear and is about a millimeter wide) weldable, how much would that cost if it is, and should I just try and replace it?
There are LOTS of cars in the area up on craigslist with parts, so if I have to get a new one it shouldn't be a biggy, but It'd save me from having to dismantle some stranger's car if I could just get this one welded.
Let me know what you think.

I wouldn't recommend welding it. The part will warp and you won't be able to get it back proper. Either get a replacement slip yoke or find a used drive shaft.

There's sort of a karmic rule when it comes to things like this. No good can come of saving a few bucks or a little effort by welding a cheap and common part.

just got a whole rear driveshaft including yoke from a 1997 Blazer for $25 on craigslist, picking it up tomorrow. :)
Now the question is, if both ujoints on the driveshaft are good but OEM, I already bought the ujoint should I replace the rear one anyway to prevent having to do the whole job again later? Or, I can just put the new driveshaft back as-is and just take the ujoint back to NAPA and get my $26 back (more than the whole driveshaft, lol). Oh, do you think it's my fault that mine cracked? Did I do something wrong or do you think it may have been cracked before, related to the failure of the ujoint.

I would replace both of them while you have it out. It doesn't take that much time and you won't have to wonder.