Corvette had not been out for three weeks, so backed-out of garage, pushed clutch pedal down to shift into 1st, pedal stayed on floor.
Pulled pedal up with foot. Pressed pedal down again, put into 1st, pedal came up. Drove for about 10 minutes, parked for 2.5 hours.
Return to Corvette, pulled-out of parking lot, clutch pedal all good. Drove for about 15 min, then pulled into a parking spot, pushed pedal down and it stayed on floor.
Returned 10 minutes later, pedal was fine, drove 7 minutes to home. Pedal was fine.
Removed clutch reservoir cap and....ugh, dark fluid. Wow I had done a complete flush 1.5 yrs ago, only drove it 1k miles at most.
Ok, time to flush again. I have a slave bleeder.
Got wife to help and every time she pushed clutch pedal down and I opened bleeder valve, pedal stayed on floor.
We kept doing this until I had clear fluid coming out of bleeder, but not once did the pedal return on its own.
And yes the spring is there and not broken.
I see no fluid leaking, but did not lift and get under it yet.

Have ordered a master cylinder and have a lot of hope it is the master and not the slave.
Only have 32k miles, but I know it is just as much time as miles.
Master cylinder will be here on Monday.

Sooooo....what do you guys think??....master or slave??

 

50/50 hope it's not the slave, good luck

 

New clutch master solved the problem....however it created a new ones.

I used a LUK LMC372 clutch master cylinder as listed by RockAuto, supposed to be the same as OEM.
After install, found the clutch safety/start switch is not depressed and clutch engagement point is much high. Only need to depress the pedal about 1/3 as much as I used to.

Did some searching on here and found that this is the problem with the LUK LMC372 master, it is not the correct one.
I will be removing it and getting a different one.

 

There can be times when the OEM is the best option. The GM 12564455 is that best option. There are many fans of the Tick, but it will increase pedal pressure and requires more work to install.

 

From reading on the Forum, even getting the GM part is not a guarantee.
Seems that LUK makes the GM part and one member on here purchased the GM part number and apparently received a LUK LMC372, which of course had issues. He then contacted LUK about the issues and was told they would send him the GM 12564455 spec'ed part. But he did not reply after that.
I have ordered one from O'Reilly Auto Parts as other members have had luck with off brand aftermarket master cylinders.
If this one does not work, then I will get the GM part.

The LUK LMC372 will work. It is a bit difficult to install as it does not twist into place by hand, I had to use a wrench to get it to twist and lock. Then the issue of not depressing the clutch start switch, which I just used my foot to depress the switch the one time I did go for a test drive. Lastly, the pedal is a bit higher, and the engagement point is higher, requiring only about 1/3 the pedal travel as before to shift. I can just set my left foot on the floor and work the clutch by moving my ankle. No need to lift foot to use leg to push clutch pedal down, does not require that much travel.
However, there is no slack in the clutch pedal, seems like the throwout bearing is staying in contact with the clutch springs. This would likely cause the bearing to fail sooner and possibly not getting full 100% clutch pressure plate onto the flywheel.
Corvette is once again parked in garage until the next master cylinder arrives.

 

The clutch master cylinder from O'Reilly Auto Parts was a perfect fit and function. Same price as the LUK unit from RockAuto using the 5% discount code, including shipping. Although RockAuto seems to collect more sales tax than it should.
The CM1327 master from O'Reilly Auto has a metal cylinder rather than plastic like the OEM and LUK.
Only other difference is the pedal seems just a tad bit firmer than the OEM. This may be that the OEM was leaking internally, so not as much pressure...do not know, although I may cut the OEM one apart to see what it looks like.

Anyways, back on the road again.

Later,

 

Good info on a replacement master cylinder, my 97 is a 6 speed and hoping I don't have problems for a long time.

 

Your experience with Luk LMC372 is interesting... I installed one back in Sept. 2020 and ran it for 10 months & 3300mi, only uninstalled because I replaced it with a custom master cylinder setup (similar to Tick, and with stock bore size).
The Luk MC worked just like the original/stock MC as I recall, no issues or surprises. Still have it on the shelf if you're interested in comparison pictures.

I think the clutch MC is supposed to have a sort of relief or bypass when fully extended, which if working I imagine should have given you a lower pedal engagement and contact with the lower clutch switch... maybe it wasn't working or something.

Great info on the CM1327 ! I hope it lasts a long time.

 

Hopefully the CM1327 does last; did come with a lifetime warranty and pretty easy to change-out once you have done it once.
The LUK and the CM1327 are configured the same way, no new metal line to the slave cylinder, so do not have to mess with that joint between master and slave.
Which is another reason why I did not get the GM part...it comes with a new metal line and a new plastic reservoir. Did not want to have to try to get the master to slave line joint apart. It is rather difficult to get to.

I sent the LUK back to RockAuto for a refund.