70 front wheel cylinder

[71tahoe]

I'm redoing the front brakes on my 70 GMC and found one of the wheel cylinders leaking. I know. Imagine that, a 40 yo truck with a leaking wheel cyl. The trouble I'm having is finding one that will fit. I could be wrong but I believe all the big name discount parts places use the same local warehouse or just packaged under a different brand. So the first one I got yesterday that didn't fit (yes I returned it and got my money back) will probably be exactly like the one they get in today, will probably be just like another one from "The (twighlight) Zone" or O'reamme's.

Is it worth the effort to rebuild (I think I have 3 to chose from)? If not, who makes one that will fit?