Clutch Slippage - Troubleshooting prior to replacing

[dogsridewith]

Interesting.
+1 to posts here noting air in the system would tend to keep the clutch engaged...not make it slip.
And there's no real obvious or common way a worn slipping clutch would somehow fix itself.
But what if water water got into the slave cylinder the way air apparently does with some regularity on these. Causing rust and hanging up the slave piston so it doesn't fully retract and let the clutch disengage? Then the fluid change at your bleeding was just enough to progressively improve things a little in there.