Im an opponent of the stock clutch line. the stupid flow restrictor is made of plastic and brake fluid makes it very sticky over time. used to screw with my clutch pedal real bad. like would leave it stuck down. ultimately my slave was on the way out too so that was definitely playing in to it.
best case scenario is your brakes wore down and sucked up brake fluid or there is a leak in the line.
IMO its likely that your slave is going bad. Especially since you cant get it into gear. You can try bleeding the slave. If it keeps taking on fluid or air bubbles come out when you bleed the slave I'd say its time to pull the trans off and replace it. hopefully the other recommendations work.
Could very well be the master.
The way I troubleshoot this.
Check bellhousing weep hole for fluid.
Check top of trans for fluid
Check by the pedals for fluid in the car.
Then, Top off brake fluid, bleed clutch, see if it even build pressure.
Look for leaks.
If theres no leaks, and no pressure. I replace the master cylinder, and suggest replacing the clutch soft line.
If after both those, you still have clutch issues, THEN it's time to drop the trans and do the slave.
Dollars, to effort, to time down. Clutch master first, always. Its like a 70 dollar part, and an easy install.