The master cylinder exibited this exact behavior in my '84 a number of
years ago.  I changed the crappy brake fluid and haven't had the problem
since (same master cylinder).

YMMV

Mikel
Houlton, Maine

Edward Maglott wrote:
> Master Cylinder.  The rubber seals in there sometimes exhibit this
> sometimes sealing, sometimes not symptom.  Especially likely if you find
> the level of brake fluid is not dropping.
> Edward
>