IIRC # 12 goes bad due to lack of lubrication. There was a few threads about this long ago.

 

#12, #13 and #14 can go bad due to lack of lubrication.

^13

^14

The S2k gearbox makes noise because you're sitting right next to it.
Did the noise become worse over time?
When was the last time you changed trans oil?

 

So what was the final diagnosis. I'm dying to hear what you found when the gearbox was disassembled.

Chris.