Has the buyer already left feedback on the transaction! I think that two months is TOOOO long of a time to expect a refund or repair cost.And you know in your heart that it tested out OK.I would just tell the guy that it just has been too long and there is nothing you can doat this time to assist in the cost of the repairs.Not your fault a shop has waited until now to say it is bad! Maybe they hooked up something wrong and burnt it out.I don't think you owe the guy anything at this point.
Bobby Dodson