Facts: After the handover of a used car, ugly rust spots appear under the paint on the tailgate, which could not be removed even after several repair attempts. The buyer is generally satisfied with the vehicle, and the rust does not bother him, as he intends to use the car for spare parts anyway. The only annoyance is that the tailgate cannot be sold, and repairing it would be uneconomical.

Question: What options are available to the buyer?