Id confirm your gear ratio. Also check the shims like jjvw suggests. This is the best picture I have of stock shims that are noticeably thicker.
Our buddy took a look and guessed that maybe you do have a thin shim from factory (hes seen them before) and that it was nicked just enough when you put your new shafts in that it caused it to catch on something and finally tore apart
View attachment 63707
My wife picked it up at the Southwest Mall here in Littleton. Tungston in what I would call a brushed silver outside, inside is gold colored.
I will start with that. Gear ratio should be stamped on the gear, right?
Does your friend does this for work and would want a new client? Is the cost to have a shim like this replaced almost worth it to just upgrade to new gear ratio since I'm guessing the carrier has to be out, or is it cheap enough that it's worth just replacing the shim and saving the money till next year.