Maybe we need to take a step back and ask some basic questions like why didn't the OP check the private key when he first got it to make sure it was valid?
There are a lot of red flags here which make me think this is a scam, from the "seller" sending OP a raw private key instead of making a transaction, through to the key containing invalid characters. However, there is nothing OP can do about any of these red flags now, and we can only attempt to work with what he has in his possession. I strongly suspect OP has been scammed and there are no coins to recover, but we can at least try.
If the private key cannot be validated then dispute the transaction with paypal get your money back. post on the forum that they tried to scam you. etc. etc.
You can correct me if I'm wrong (since I've never used PayPal), but my understanding is that there is a time limit of 180 days to open a dispute. PayPal are not going to entertain a dispute for a transaction which is in the region of 10 years old.