The Daughter’s ‘84

[ArdWrknTrk]

I don't think that glycol evaporates.
As a clutch wears the fluid should get higher, not lower.

But I'm really glad to hear that it's functioning now.
Do take a look at the master pushrod where it connects to the pedal arm, and have your daughter press the clutch while you look at the master from the engine bay to see if the firewall is giving out.

[Atlas75]

Brakes failed today.  I crawled under the truck from front to back and couldn't find anything wet.  So I went up top under the hood and the only thing I can find is some wheaping where the master cylinder mates to the booster.  There is a 1" wide area under the master going down the booster.  I'm guessing the master has gone bad.  How does this affect the booster?

[ArdWrknTrk]

Unfortunately, brake fluid will eat the booster diaphragm.
Usually you will hear hissing under the dash.

Did you look carefully between the midship tank and the frame rail, and also where the hard line pokes through the crossmember to join the hose to the rear axle?
Rust through is most common in these areas.

Ideally these problems are easy to fix with the new copper/nickel line.