If it's sat outside for the last couple years, the first thing I'd do is replace all the bearings on the clutch shaft. Believe me, you don't want to spin them and replace that shaft. Next; check the bottom of the feeder house floor. That wears through and piles straw and chaff on the hydro and the combine goes up in smoke. Check the pivot bearings on the feeder house. They normally don't get greased properly and can be worn. Rubber bushings that drive the shaker shoe should also be replaced regularly. Check the drive gears for the accellerator rolls and the rolls themselves. Bevel gears that drive the straw spreader deserve a look too. Check the pivot shaft for the rear axle, make sure there are no cracks beginning where it welds to the axle. Check the cage for spots that have worn through, check the helicals on the inside of the cage. Check the gear case that drives the cyl. Make sure the inner seal isn't leaking, and check the condition of the oil in the gear case. Ed in Montana