Upload & Sell: Off
Yes, you should attempt to return the lens and congrats on winning the dispute (AmExp is great for this).
BUT!!! Do not eat the shipping. Not only should he pay, but make sure he pays for delivery confirmation, tracking, insurance, etc...
If he refuses to pay return shipping (collect BEFORE you ship), then refuse to send.
Keep us updated.
I would also give him a deadline to respond / pay shipping fees.