1996 LT-4, had problems with the clutch slave cyl when I had the clutch replaced. Finally got a slave that didn't leak after the fourth one. I have diven car for 12k and now when I push in on the pedal, it leaks down a bit when I hold in the pedal. Shifting is no problem. Only when I hold it in. Question wether its the clutch master cyl or slave. The fluid is full in the master so I don't think its leaking.

When it "leaks down" will the clutch start to re-engage? like say your stopped sitting in 1st gear of the brakes will it start to roll on it's own after holding the pedal?

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Yep, Rick's right (as usual).
The test is to find a level spot, put the car in gear and hold the pedal in for 30+ seconds. If it starts to roll, it's leaking down.

GM had a major problem with the slaves back about 5 years ago... the problem spanned several years, too. Say, 2002-2007? That sounds reasonable.

The problem? The main seal in the slave was installed BACKWARDS. This caused a ton of blow-by and lower piston pressure. The other issue is that they were assembled as a kit - master, slave, line, prebled, in a seal package. The problem? Moisture would get trapped in there and cause all sorts of issues... mainly, pitting on the bore of the cylinder

When I did my clutch 18 months ago, I replaced my slave with one from NAPA. It is a very quality part, made in Taiwan. The slave body is one piece, cast, so there is no seam to leak from, and the seal was installed correctly! So much so that I have not any reason to add fluid to the clutch since that change was done - 18 months ago! The mileage isn't much, about 4000, but time sure would have found a leak by now. The last time I checked the reserviour, oh, 2-3 months ago, it was still on the high mark. Me happy.

Do what Rick and Bill suggest. Great starting point. When done, jack up the car and inspect the slave and the line for fluid loss. You could have a weapy o-ring on the hose, too. Check for moisture on the slave and the surrounding area. It should be dry.

Remove the PCM and check the master for fluid leakage. Check the hose, the area around the firewall - it will weap out of there, and inside the car, where the master comes through.

Sometimes these leak throughs are internal. It's simply leaching past the main seal... but not leaking out.

In short, I think you have yet another bad slave. Sorry...

Regardless of which component has failed, you need to inspect the replacement carefully. I can't count the C4 cluch hydraulic jobs that I've done, but every single replacement part (master or slave) had crap in the bore out of the box. It doesn't matter where you get it or who makes it; there is junk in the bore every time.

Take it apart (the only 'specialty' tool you'll need is some snap ring pliers) make sure the seal is installed correctly, clean the junk out of the bore, and install.

My ac delco master had metal slivers stuck on the seal.

And the slave, even if you get a correct one, the aluminum piston can corrode and pit the steel cylinder pretty quickly, ruining the seal.

The clutch will start to re engage if I leave clutch in after about 10-15 seconds. I was just wondering which one since I have had so many in the car. I had a well known corvette shop in the DFW area install it. It was suppose to be a slave that was checked.
By the way, THANKS for the replys, some of the other forums don't answer.

I am glad you got some info to go on.

The info shared here is a) FACTUAL and b) empirical. We have all had issues and it was CentralCoaster who found the seal problem 4-odd years ago.

As a seperate FYI - Rockauto has a Sachs master cylinder on closeout for $43.00. I am tempted to order one.