Stick a cheater bar into the PTO shaft and see if the machine turns or if it is froze up. Chains can be oiled and worked loose, even pretty rusty ones. If it turns, check to see if all the systems move or if some drive chains have been scavenged off for parts. If you buy it, get in contact with jdtom for an owner's manual, which will have the grease pattern for the machine. Trust me, there are grease zerks on that thing that you will never find without the manual. You might check the bearings at the top of the snapping rollers for loose play. Open up the gear boxes (3 or 4 of them, if I remember correctly) with a wrench and see if they hold oil or are dry and rusted. Check to see if you have both upper and lower gathering chains on both sides. It wouldn't hurt to look at the rubber picker fingers--they can be a bit expensive to replace if too many are broken off. Don't worry about the paddles on the main intake chute or the elevator--you can make new ones pretty easy with a press and some plate steel. Replace the rubber on the paddles with old belting. You are going to want to stock up on replacement chain links, especially the ones that attach to those paddles on both right and left sides. You might want to stock up on some bicycle chain, too, including splice links and half links. It wouldn't hurt to look underneath to check for stress cracks in the main support beam holding up the elevator base. There are a lot of other things, but this list will get you started. Others on this forum know a lot more about it than I do--some of them will probably chime in.

I've got a 325 gathering unit with a 329 sheller. Bought the sheller a couple years age from the dealership that has had it since it was new (about 30 years). I also have the 327 12 roll husking bed and the 318 grinder unit. There are only 3 zerks on the sheller. There isn't a whole lot to look at except the bearings and check to see if anything is rusted out. I have a parts sheller if you need parts.