Dreaded slave cylinder fail?

Seem to have lost the clutch in my 87 US spec cab this morning as car won’t shift into any gear when running. I of course suspect the slave cylinder since I haven’t touched it in 6 years of ownership. Pedal still feels as firm as ever. Is this typical when you lose the slave? I thought the pedal might just go to the floor and stay there. Are symptoms of the clutch master similar or is there a way to tell where to look first?

 

Upon further inspection, there is fluid on the slave, but it also is still extending, though not very far. I have no idea how far this thing has to push the linkage to operate, but I would guess I’m only getting 1/2 to 3/4 inch of travel. Do these things die slowly before going completely belly up?