I sold a recreational vehicle and he signed a bill of sale and took it off my property now he wants extras with it or will sue

I sold a recreational vehicle it had a signed bill of sale and he took it off my property when we were talking i said i may have some extra parts and I would send them if i found them. I couldnt find them now he wrote a letter saying if i dont pay their value he will sue me for the price of the parts. These were never included in the original ad to sell the vehicle either. can he sue me