A couple of things...make sure all the chutes that guide the seed down to the discs are there. Every disc has a bearing it rides on, make sure they aren't hooped also. You might want to check to make sure the adjustment that sets your seed flow quantity is not severely rusted into place. This might not really matter too much since it was ostensibly set correctly for at least one grain when it was last used. As art said, check the inside of the hoppers. If they weren't cleaned out after last use, they might present problems. Check all chain drives and sprockets for excessive wear. Try to inspect for missing parts if possible, i.e. tension springs for the discs. Inspect the tires for cuts excessive cracks, etc.
It would really help if you had a friend/acquaintance who was familiar with farm equipment and whose judgment you could trust accompany you when you do go look at it. If you don't know anyone, maybe you could ask around and see if you could find some Olde Phart who would be willing to share his knowledge.
