Ideas? Sticking clutch pedal only when braking heavily

[Oldcarguy]

I know a sticking (on return) clutch pedal can be a symptom for slave going bad, air in lines, clutch bearing, etc. but I’ve got a slightly different manifestation.

Under normal and spirited (heel and toe) driving I have no clutch pedal issues. Smooth engagement, proper pedal travel, etc. Clutch has ~4,000 miles on it since rebuild by PO’s independent shop.

However, when braking extremely hard with the clutch disengaged simultaneously (classic ‘panic stop’) the clutch pedal returns halfway and sticks. If I depress it again, it returns normally. I discovered this because I occasionally engage the abs on purpose to exercise it. But sometimes the pedal will also stick under very heavy braking without getting into the abs. Brake and clutch pedals are firm.

I’m going to purge the brake/clutch fluid (with Motul 600) and see where I’m at. If nothing changes regarding the sticking pedal, looks like I may be headed for a clutch slave cylinder replacement next. I need this fixed before I put the car on the track for HPDE events.

Any thoughts?