Unhappy buyer .What to do ???

After 2 months of silence you can feel fine in saying "Sorry, but no." Its used and who knows whether that chunk sat on a shelf or did 30 passes since you saw it last. Personally I would never buy used gears, to much of a roll of the dice, and since he decided to roll the dice its now his problem if they come apart. Your ad was very clear about what was being sold.