[Spits] Replacement clutch master cylinders?

[Doug Braun]

Hello,

My clutch master cylinder is starting to leak again. 
Over the years I've rebuilt it couple of times, and it
always seems to start leaking again after several
years.

So I'm thinking of just spending the $$$ and buying an
entire replacement MC.  I saw that Spitbits sells an
OEM MC for about $120, and an aftermarket version for
half that.  Does anybody know what the difference is?
Also, is an OEM version likely to have been sitting on
the shelf for years, and need a rebuild before it can
actually be used?

Thanks,

Doug Braun
'72 Spit