Funny how often it's the cheap stupid stuff, but here's the angle nobody talks about - bad U-joints can actually mimic a death wobble. Had a buddy spend two grand on steering stabilizers and track bar bushings trying to fix a shake at 55mph. Shop told him it was everything except the U-joint, probably because they wanted to sell bigger parts. Replaced that $35 part and the truck drove straight as an arrow. Another thing nobody checks is that seized U-joints will wreck your axle seals over time from the heat buildup. That little click turns into a leaky diff pretty quick if you ignore it long enough.

Ever actually watched someone try to move a crane with a joystick?

Oh man, tell me about it! I had a similar thing happen with my old Panasonic deck back in the day, except it was the motor that started making this godawful grinding noise. Turns out a little plastic gear inside had stripped some teeth after years of use, and I spent three weekends trying to track down a replacement before I gave up and just bought a whole new unit from a thrift store (which honestly worked better than the original ever did, go figure). I still have the old one sitting in my garage waiting for me to find time to fix it, because you know, someday I will totally get around to that. Your flashlight trick for alignment is genius though, I always just eyeballed it and hoped for the best, which probably explains a lot of my past belt failures.