Hey Olylawnboy,
If you don't have confidence in the integrity of the Master cylinder i'd just go ahead and replace it........The seals do breakdown after time..... not as fast though due to not being exposed to heat as the wheel cylinders are........
Brakes are paramount......gotta be reliable.......Check those rubber hoses too..... they may look good on the outside but the inside can start collapsing causing obstructions and eventually brake failure.....

I just found one of my rear lines that had collapsed....... Brake Fluid came out real slow.......... I replaced the hose and it flows stong...
There are good new ones on the market..

.. I haven't seen kits in a long while either....