It is never wise to accept a replacement, money back guarantee would only cover first item, there would be no ebay protection for replacement.
The money back guarantee only applies for 30 days from delivery,so you might have been too late, in which event the seller could reject.
If seller was a private seller, they would not have to accept a “does not fit” return, but a business seller can only reject and close casecif outbof time.
I doubt that whatever seller says you will ever see a replacement, so best to see if your payment provider can help.