I searched around for a while but I haven't found someone with a similar issue yet. Hoping you guys can help me out.

On my way to work yesterday I stopped being able to shift into any gear with the engine running. The pedal had hardly any resistance to it and the car would slowly roll with the brakes off, in 1st, but with the clutch depressed. Long story short, I get a tow home and also pick up a new clutch slave cylinder, considering it's the most likely culprit. I picked up a vacuum bleeder and get to work today, but I went through an entire bottle of brake fluid and still had air in the hose. I don't see leaks anywhere and everything else looks fine, I just can't figure out where the air is coming from. The reservoir drains as I pump the vacuum, otherwise it doesn't go anywhere.

The vacuum pump eventually gave out on me so I ordered the Motive Pressure Bleeder and it'll be here tomorrow, but is there anything else obvious I should look for? Could the master cylinder be dead instead of the slave?

 

Did you use a tool to compress the slave cylinder piston while bleeding?

 

Yes, the slave was fully compressed.

My best guess right now is that air was coming in through the vacuum pump line at the bleeder nipple. Hopefully the pressure bleeder will do better.