Have a good look at the add especially if you got it from fleabay as sometimes it is listed as new (up the top) then later on somewhere in the description it may mention reproduction just read it carefully if it is a bona fide repro approach the seller for A) Cash reduction in purchase price C) Return the item at their cost they add the postage to your refunded purchase price.
But seriously look at the advert if an amicable solution is reached then there is no need to go to the disputes part.

Or you could accept it for what it is plonk it on the rifle and carry on slinging lead then you may happen onto an original at a cheap price hey presto rifles back to near original and you can always flog the non original but list it as such having been in disputes on fleabay sometimes it is just not worth the effort protracted and messy.
Or get the original repaired re-parked or blued and there you go........your call.