Regarding your transmission IHMO it's nowhere near as bad as you are imagining.
I wouldn't even consider removing it for teardown & evaluation without FAR MORE in the way of diagnostic confirmation than you have right now.
All I'd do personally is throw new oil & a filter in it, then change oil & filter again a month down the line, and keep getting regular oil samples to establish a trend.
If your current machine is repaired, you have a known quantity.
If you trade it for another machine (I assume a used one), then you start again from square one with an unknown quantity, which I think is where we came in 4 pages ago ........ YMMV.
Check your PM's.............