First you contact the seller and ask what he will do to make this right.
If that is unsatisfactory:
After 45 days forget Paypal and eBay. Go to the credit card that your Paypal payment was processed from, call the Customer Service 1-800 number on the back and ask about a chargeback.
You will need dates, PP transaction number, eBay transaction number and the date of the transaction for the clerk to process the refund.
You may be required to return the watch to the seller with Delivery Confirmation.
You have up to 60 days to leave feedback and Detailed Seller Ratings. The seller should worry most about the DSRs.