During a track day at the weekend (Cadwell, brilliant fun) my clutch seemed to progressively get worse until I could barely get it into first from neutral.

Opening the slave cylinder bleed nipple and pressing the pedal gives a little bit of fluid dripping out, NOT a decent spurt as I would expect (and have seen in the past).

I think this must either be the seal in the master cylinder, OR, it has somehow ingested air during the track day (unlikely as it's a high-up remote reservoir?). My plan is to disconnect the hose and replace with a solid bolt into the master cylinder, then see if it is solid or not, to see if the master cylinder is functioning properly?

Any suggestions?

Check the pedal is allowing the cylinder to fully return, before you dismantle too much.

Well, I've blocked off the master cylinder and it went rock solid so it's either air in the hose, or it's the slave cylinder.

I've ordered a vacuum bleeder (can't get the easi-bleed to fit my reservoir) which will hopefully do a thorough job of bleeding it - if that doesn't work then I guess I will have to replace the slave. Let's hope that's not an engine out job. I will not be happy if it is.

Hmm, several hours with a vacuum bleeder and I've bled the poo out of it with very slight improvement, but still not working (you can tell it's just on the edge of engaging when I reach the end of pedal travel).

So I tried unscrewing the master cylinder a couple of turns out of the pedal and the clutch works now - right at the end of the pedal travel, but still, it does the job.

Not really sure what's changed to make this change necessary. Could it still be air in the system? I couldn't find any leaks. Faulty slave?

If the piston doesn't return to the start position in the cylinder it doesn't allow fluid into the cylinder from the reservoir so it won't work properly. It sounds like you had no free play in the system.

Nope, not that - it's been able to return freely at all times. Unscrewing the m/c a bit has just given me more stroke so when the pedal moves, the m/c is pushed a little bit further.

My current suspicion is air in the slave - apparently on the E36 gearbox, the bleed nipple on the slave is at the bottom so it's very hard to bleed. When I get a chance I'll dismantle the centre tunnel, remove the slave and invert it while I bleed it.