$476 to assemble an 8 3/4 diff

I did ford 8.8s at the dealership, I agree not brain surgery. That's easy to say but they are easy to mess up also, I've seen young techs screw up tires, brake jobs, typical beginner stuff. I once saw an idiot drain the trans and overfill the oil on a Subaru. Another idiot says to me "I forgot to put oil in that last car I had in" I say "well go put oil it it, he says "I cant there it goes..." and we watch it drive down the street. I said "It will be back inside a half hour...' :)

"I've seen young techs screw up"
Exactly, and that is why I do my own work. Even if I have to buy special tools or instruction.
And I am not saying that I never made a mistake, I have, but it is then, my learning opportunity.