That aint right selling you an unusable part.
Hopefully he sold you the correct master for your car, disc brake A body would have a casting number 2225541?
I just looked at the one I have and compared the lid to the ones used on disc brake B bodies from 67-'70 and the caps sure look the same. My 2225541 sample is an NOS assembly line piece so I don't want to mess it up prying the lid off to confirm the rubber seal is indeed the same but I'm 99.5% sure it is! The Bendix seal used on the B body lids has a part number 2225441 molded into it. Raybestos and Napa sell a B body disc brake master cylinder that has the correct lid/seal and it's part number is 36283.
It would suck to have to spend $50+ for a new MC just so could pirate the seal though.
I did a quick look online and didn't see a rebuilt version, if those do exist the cost would be around half new and it would have a new seal to take from it.
Napa sells an assortment of MC caps and MC reservoir gaskets. I did a quick look at their website and saw a MC reservoir gasket p/n UP 23583 that looks correct but they give no dimensional info so I can't tell for sure. I have a 36283 sample and the cap gasket has a part number 221023 molded in it. Of course you'd want to take your cap to the store and see if that gasket fits correctly regardless of what number it has molded in it!
Let us know if this info helps!
