C4 brake master cylinder

Glad to be a part of the forum now, guys and gals.  Just signed on and have a quick question regarding a brake issue that recently developed in my ''88 coupe.  Unfortunately, I''m in the middle of a move right now and don''t have access to the equip and tools I need to work on it myself, so I''m at the mercy of a local mechanic.
 
Occasionally when I come to a stop, the brake pedal goes almost all the way to the floor.  It doesn''t happen all the time.  Pumping the brakes restores the pressure and tightens up the pedal.  The brake light will sometimes come on in conjunction with the pedal softness.  I know my pads and rotors are fine, the fluid level is topped off (and clean), I don''t have any unusual noise or alignment issues. 
 
I''ve been told that this is a sign that my brake master cylinder is bad, and that the seals between the resevoirs has developed a leak that is causing the fluid to shift from one chamber to another resulting in increased pedal travel.  My questions are (1) does this sound like a good diagnosis of the problem and (2) is there any solution other than replacing the entire master cylinder (ie, is it possible to repair only the seal)? 
 
Any help with this is appreciated!

My questions are "(1) does this sound like a good diagnosis of the problem and"
CG - Yes.
 
 
 
(2) is there any solution other than replacing the entire master cylinder (ie, is it possible to repair only the seal)? 
CG - Most times master cylinders are not rebuilt, but replaced. If you could find the seals only it would be possible, but it is far too convenient to replace the unit with a new one.

IMHO... its just easier to replace and core the old one.  A lot goes into a rebuild... they hone the piston bore, replace all the parts... check for stripped threads...  just easier to replace it I guess.  And... whats your time worth?  It eats up a bit of time rebuilding one...  at least a sixer too...

I doubt the master cylinder would be too much to replace and it is an easy install.  But it definitely sounds like that is your issue.