Yes, just start a claim, now.
On sellers, a question: besides the other 2 Leica lenses, does the seller specialize in cameras? Or was it a one-time find he's selling? Ebay is a virtual garage sale, it is NOT A RETAIL STORE! People sell things all the time they know nothing about, that they found or inherited. They don't know if the tube radio works, they don't know a cast iron skillet can warp, they don't know if the coin is a forgery. That's just the way it is, no one can be an expert at every single item every made by man or God. No one but a photographer would shine a bright LED light through a lens at angles, looking through a loupe. He probably didn't see the problem.
Before Ebay, you'd go to a flea market, or a guy at a yard sale would be selling a camera. You'd handle it, and determine, as the expert, if it was worth the asking price. If you got burned, you got burned, and didn't usually try to go back to the seller. Because he was NOT an expert. Today, online, you cannot handle items, so there is the problem.
If it was a "camera seller" then that's a different deal, he should know better. Either way, no one likes to have to give a refund. But after they (usually small time seller) realize camera people are very picky and need fantastic condition optics, they are usually more careful next time they sell a lens or camera. I'm telling you, in the 5 or 10 areas I buy antiques, camera buyers expect the most out of a 60 or 75 year old tool. You gave the guy a chance though, now just make a claim and let ebay give you your refund.