Some Nuclear Physicist! Can't even figure out a clutch pedal! Good thing
Little boy didn't burn the atmosphere!  ;)

At any rate, I would look at a couple of things. From what you're
describing the first thing I would look at would be the pin that holds the
clutch pedal onto the bracket. It may have some teflon or similar plastic
bushings and they are wearing out. Or, the pin or the bracket my be
rusting (this has happened to me before, and if it's getting wet, you have
bigger fish to fry. On one car it was caused by a windsheild replacement
that just would not seal, and on another it was because the windshield
frame/cowling/firewall was rotting out and allowing water into the car)

The next thing (or, perhaps, the first thing) is the spring. It may also
have gotten wet, or has shifted and is binding against itself somehow. It
may need to be 'reseated', which means merely moving it back to where it
should be without removing it. I would also grease while I'm down there.

Also, check the connection to the plunger that runs through the firewall
to the clutch Master Cylinder, and check the boot, too while you're at it.
The boot may be allowing water onto the plunger and again, may be rusting
where it is joined to the pedal. Check for bushings and grease it if you
can.

Beyond that, we're into the Master Cylinder, and it may need replacement.
But I doubt it goes that far. More likely one of the other things I
mentioned.

Good Luck!

Grease the pedal return spring.