Why did the buyer wait so long after receipt of motor to inspect? Why did he not immediately return for inspection/refund?
I am not in control of this buyers decision. nor anyone's but my own. I empathize with buyer in having a car down, I sympathize with buyer that his secondary means of transport also broke during this period, but that is not my responsibility.
I offered buyer the same warranty and repair I offer all of my customers. If you have a problem with anything simply bring it in or return it and it will be inspected and/or repaired as necessary. If a refund is desired simply return the item in unused condition.