when I got my 8820 I changed the reverser oil, final drives, transmission, hydro, hydraulic, two speed cylinder. in the hydraulic and hydrostatic tanks there is a filter.
got a new copy of the owners manual and made sure I could find all the grease zerks and they all worked.
start at the front and just take piece by piece. feeder house check the floor tins, chain tension, find the S clips on the feeder house chain and make sure there still good, top shaft sprockets and bearings. cylinder and concave, belts... just work your way back. gear box on the grain tank fill auger, I would put a half tube of grease in him, same with gear box on unload auger elbow.
get a winter inspection form from the local dealer and use it.