I had to replace the gearbox on my deluxe maxxfan... it wasn't that hard. rather than trying to work on the roof of my 21, I took the whole assembly off and did the repair on the bench.
to get the thing off, I manually lifted the lid, then you remove 2 screws on each side. on the inside, you remove the screen, bezel and then you can unplug the wires. also remove the knob. now you can lift it off the roof. I put a towell down next to it first, so I could put it on the towel so I could situate myself to carry it down off my 8' ladder.
the instructions that come with the replacement gearbox show how to remove it from the fan assembly (they assume you are doing it on the roof of your RV, but are still applicable to doing it on your bench)
The part I replaced is 10-20281K-1AF, I got it from etrailers, for $13.... ooops, looks like its $16 now. https://www.etrailer.com/Accessories...0281K-1AF.html
2014 Escape 21 (home away from home)
2002 Ford F250 7.3 Diesel 4x4 (tug)
1993 Mercedes 300CE Cabriolet (daily driver)
2006 Yellow Lab (Maggie... RIP Feb 2019