Dan Burtt
Similar to the other reply - I have replaced mine with a NAPA rebuild and it has now held up through 5 years of use and abuse on a car that I drive in competition. The clutch is a Sachs performance clutch and I have the original 4+3 trans with the OD locked out. This car does not get driven gently and I have had no issues with this clutch. Not sure what fluid your mechanic is using, but any good DOT 3 brake fluid should work. I use Valvoline synthetic DOT 3 & 4 fluid which seems to work well. As also stated above, these suckers are a bear to bleed and I end up bench bleeding it using the little tubes that usually come in the replacement kit before attaching the lines. The problem is the little uphill bend they put in the tube and it acts as a P-trap for air. Later C4s didn't have this issue and are easy to bleed.
As with any system like that - the key is to keep it clean. Worst case, and if you don't mind spending the bucks - take it to your GM-Chevy dealer and let them figure it out - they have good warranties on their work.
good luck!
There is no problem a little horsepower can't fix!