Question about soggy clutch

Bought a 92 Toyota Corolla from neighbor and he told me the clutch was
going bad but what I've found is the clutch pedal sinks so obviously it
would seem to be the master cylinder is going out right?

But, BUT before I go out and replace the master cylinder, I wanna run
this by you folks out there that know these things better.

Basically when the tranny is in neutral the clutch holds pressure
completely but once I'm in gear the clutch starts losing pressure BUT
only after I've let out the clutch; MEANING that as I'm holding the
clutch pedal down and I shift into 1st gear and I push the pedal back
and forth BEFORE THE FRICTION POINT the pressure holds just fine. But
once I let the pedal out to the friction point, then I can feel the
clutch lose pressure. In fact at the friction point I can feel the
pedal lose pressure immediately. Thus when I'm having to clutch in
either 1st or 2nd gear in heavy traffic I can feel the pedal heading for
the floorboard. To get the pressure back I have to put the tranny in
neutral OR let the pedal all the way out and the then I get my pressure
back.

Checked the slave cylinder and there's no juice dripping out of it.

So: is it the master cylinder or something else I'm not aware of.

Thanx in advance.

It's one of three things: The master cylinder, slave cylinder or the
hydraulic line. My first choice would be the slave cylinder because it
is exposed to the elements.