Check rotor coupler and splines on rotor gearbox, check spindle bushings on rear axle and wheel bearings, if it has mechanical drive straw spreader check bearings and gears, PTO bearing PTO shaft on engine, while u have PTO shaft off pull dampner off of flywheel and clean dust out from behind it. It will really smoothin out the engine. Also check engine fan for looseness. While u r checking that also check air conditioning compressor bracket that mounts to engine for cracks. Take variable speed header drive apart and clean. Take bottom panel off of the air conditioning unit under the cab and clean the evaporator and the heater core. Should really have Cummins out and set valves and injectors, recommend every 1000hrs. Check bin unloader belt, chopper belt, and clean grain elevator belt. Check u-joint in the bin loading auger and the u-joint in the unloader elbow. Make sure that u keep the unloader elbow greased. I is full off 164 balls just like a giant bearing. If it is not kept greased it will wear and the ball bearing race will come apart and the auger will fall off. Pull alternator off and blow out with air, gets dust built up under the screen. This is just a few things that are not obvious, if u have anymore questions just ask.