Nick...good luck getting through this. It's obvious someone came along after you gave him a deposit in good faith and offered more. It doesn't make sense PayPal won't read the Email string. Heck, I'd send it to them anyhow. It would make it clear you were trying in good faith to get the money to him.
The seller backed out and is using a technicality to take your money. If he'd not heard from you and had not been trying to work out the transfer of funds, it would be different. It's not like you were dogging him and leading him on. He was wrong for doing you this way. Sorry brother.
Consequently, this is why I restrict my sales to domestic and avoid international deals. Nothing bad on you, it's just too many things can go wrong. With a respected member of the CVO Harley group I might make an exception, but on Ebay...no way.
Hope you get your money back friend.