So the missus' Astra cluth has been problematic recently with getting in to gear first thing being intermittently difficult. I noticed the brake/clutch fluid was very old and flushed the entire system. Some of it was nearly black when it came out. This resolved the problem but it came back with a vengeance last night. The missus popped out and the clutch failed entirely, being impossible get in to any gear with the engine running. I met her and noticed the fluid was at 'low' in the filler reservoir so I started in first and rev-matched it to get home. Once the reservoir was topped up and the clutch primed a few dozen times the resistance in the pedal came back and it worked again. I did notice that the pedal get a little spongy after a few minutes if not used, but once a full press and release is performed the resistance returns and all is well again.
Everything points to a leak but there are no tell-tale marks on the driveway to indicate fluid is escaping. Therefore it might be the master/operating cylinder. I have yet to get it up on the ramps to get a decent look underneath but before I do what the thoughts/advice from the learned masses?