I have a noise that began on Saturday in 2nd when applying throttle light or heavy. Only 2nd gear. I took it for a spin today around the block to make a video.
I'm hopeful it is just in the tail section but maybe someone listening to the video can provide some insight.
under the car 1
under the car 2
in the car

 

Update. Looks like 2nd gear lost a few teeth. If anyone knows of a good used ap1 transmission I'm looking.

 

Good for you for finding it, I would have guessed a bad bearing. Broken gear teeth aren't common on these trannies, sucks to hear this happened. Good luck with your venture to find a replacement. I sold a mint low mile tranny a while back to Robin and then he re-sold it to someone else so I lost track of it after that.

 

Funny I eyeballed your transmission for at least a week. Lol.
Thinking I may buy a jdm engine and mission and keep the engine for a spare with the option to resell if I do choose.