My recent experience in PayPal dispute

I want to share this story with fellow Agoners.

I sold a used tube power amp here in Audiogon. In transit, a power tube was broken. I told the buyer that I could either send an additional matching tubes or accept a return with full refund. The buyer opted for additional tubes. I sent them and there was no response from him until 5 months after the sale. The buyer asked me for help since the amp had a biasing problem. The amp was almost 20 year old model.
I told him that I cannot provide any help other than trying new set of tubes. The buyer apparently wanted more helpful afterservice, and filed a dispute for return/refund to PayPal. Apparently PayPal allows filing a dispute within 6 months of purchase.
Well, he did not go through Audiogon. Anyway, PayPal closed the case in my favor. For me, it is rather obvious that the buyer cannot ask for a refund after 5 months of purchasing a 20 year old tube amp.