Technical Help Identifying Master Cylinder

So I just recently acquired a barely off-topic El Camino, a father & son project that will eventually be my son's daily driver.
I just wanted to get a new seal for the top of the Master Cylinder Jar, but can't find anything that looks like this one. You can see the winged bolt that goes down through the cover to a threaded boss in the base of the bowl.
Any help would be appreciated.

RamJet

 

I would just buy a rebuilt master cylinder....

http://www.oreillyauto.com/site/c/detail/OBH3/1040000/01292.oap?

 

Excellent, with the link and everything! $20 is pretty dang cheap. Thanks, Squirrel.

On a side note, my Father-In-Law lives in Sierra Vista.