Bought mine from a place called RV Auto parts on line early last month. $161 delivered. I got the original motor and gearbox. They make a high torque motor too. I think it was 2 days from the time I ordered until it showed up at my door. Didn’t remove my trim and it was a one man job (my mobile RV tech). Took him maybe 2 hours. He said the tricky part is marking where the chains are on the sprocket so you don’t have to make any adjustments after the install. If you have to make adjustments he said it is a real pain to line up.
Are you sure it is the gearbox? In my case I had a rhythmic thumping which was no doubt every time the broken teeth made a revolution.
If yours is hanging up in the same spot I would think it might be something obstructing the slide but that is just a guess.
Pic of the broken teeth. We could have just replaced the gearbox but I decided with the same labor charge I would be safe and do both.
Good luck.