Clutch master cylinder going out?

[BSOD2600]

My 94 wagon had a JDM 4.11 5MT swapped into in ~2 months ago. The rest of the parts were off another SS. Anyways today I parked on a steep hill, with the car facing up it. Several hours later, I got in and drove off. The first stop sign I came to (~200ft away from where the car was parked), the clutch pedal stuck to the floor. I pulled it and it popped back.

After that happened, I can tell the clutch feels softer -- its easier to depress. Additionally, the clutch engages a LOT later now. I don't think the clutch is slipping, since when driving up a hill it seemed to be ok. The clutch's master cylinder is full of fluid are there are no leaks from the hoses.

Is this a sign of air in the clutch master cylinder or the the master cylinder going out? If the cylinder IS going out, any reason to upgrade it to a WRX one?

[BSOD2600]

Well I bled the clutch and no air came out, so it must be something else.