[6pack] Foreboding brake fluid leak -servo rebuild needed?

[Pete Kronberg]

Folks,
 
My '6 has been sitting all winter. I happened to notice that the rear well of
the MC was very low, and I topped it off. Now, some 3 weeks later, after
checking it daily, it is once again empty, seemingly overnight.
 
Very wet between the MC and the servo. In past years/cars, I have gone out and
worked the brake pedal periodically to keep seals lubed and to avoid
shrinking. Didn't do it this year.
 
What's the likely culprit? Can I avoid a time-consuming, and painful MC/Servo
rebuild, do you suppose? Everything was dry and tight when I put her to bed
last October...
 
Thanks in advance for any thoughts on the subject.