Leaky master cylinder

Hey guys about a month and a half ago i bought a master cylinder from my local advance auto parts. It was a refurbished one and it leaks the same if not more then my 40 year old one... I think it may be leaking out of the top of it. It has a gasket and all on it just not sure if the bar clamp (or whatever its called) puts enough pressure on it. Also it only seems to be the rear reservoir that leaks. Any ideas? Thanks.