I know this is an old thread, but I'm hoping somebody sees this and, if possible, confirms my suspicion. About a week ago my clutch hydraulics began getting air in the line. I have successfully bled it out, restoring a firm "near-the-top-again" clutch pedal. But after driving it 30 minutes, and even just sitting overnight, I'm back where I started with air in the line. I cannot detect any fluid loss whatsoever, from the reservoir through the master cylinder down the lines to the slave cylinder (which I replaced less than a year ago). None.

My best guess is the clutch master cylinder has developed a leak -- that's the only place I can imagine the mechanics of air getting into the system with absolutely no fluid leaving the system. And, of course, I'll need to replace it and then bleed the whole thing out again.

Can anyone here confirm my guess? Add to or provide an alternative possibility?

Thanks sincerely in advance.