96 Hombre Clutch Slave Cyl. Problem

About a year ago my 96 Hombre (same as Chevy S-10) clutch slave cylinder had to be replaced, due to a leak. Within a month or two, it
developed a weird, but very occasional problem when the clutch pedal was let out. The clutch would only partially engage, and then suddenly pop into full engagement. It was a real problem at stop lights and especially when stopped on a hill (rolling backward unexpectedly due to non-full clutch engagement, then popping into full engagement, then often times stalling as a result).. Along with the slipping clutch with a sudden pop into full engagement (almost like popping the clutch, except it was usually partially engaged), there was a sort of "chirp" or "squeak" sound that at times was quite loud. It sounded like wet rubber being rubbed against glass for just an instant, and sounded like it came from around the clutch pedal itself. It was so intermittent, the mechanic could not find the problem (he didn't even experience it!), and I went on that way for many months until it got so bad I could not drive the vehicle safely.
Finally earlier this fall it was so common that I was able to demonstrate it to the mechanic (long-time transmission experts with whom I've had a very long and trusting relationship - top quality people). At first he had no idea what was causing it, and thought perhaps there was a bushing in the linkage under the dash which was catching and then suddenly releasing (the "chirping" sound sounded like it was coming from right around the pedal itself, making diagnosis even more difficult). Eventually, he went into the bell housing after he'd checked and/or fixed everything else, and found it was the replacement slave cylindar which was frequently sticking and suddenly releasing about - of the way along its travel. He actually had cleaned up the slave cylindar and showed it to me when I came to pick up the vehicle - it did indeed "hang up" at a certain point in its travel, MOST of the time. There was no leak, just a mechanical sticking of the slave cylindar, not allowing full engagement of the clutch until the cylindar released it suddenly.
Enter the 3rd slave cylindar just 2 months ago. It began to do the same thing only a month after installation, progressing even more quickly than the last one did.
From what I can gather, there should not be any alignment issues or something similar to actually cause the catching of the clutch slave cylindar, so we are assuming there was simply a bad run of that particular part, and I got two from the same batch about a year apart, as improbable as that would seem. I can't recall the brand name, though it was an old, well-known brand (my "old age" is catching up with my recall <g>), not some cheap piece of junk (or so it would be expected from that company).
Anyone have any similar experience? Even though I got the truck back again this week, I'm almost expecting the partial clutch engagement to start up again, with a sudden popping into full engagement, and want to be able to deal with it appropriately if it happens again. If not, I'm curious as heck, since even the mechanic (who I know and trust implicitly) had never seen anything like it. They've been very decent about it - two additional slave cylindar's without a penny out of my pocket, despite the fact that the original leaking cylindar was replaced in September 02 (more than a year ago).
Any ideas?!?
P.S. Please reply in the group - I rarely check this email address (it's my "throw-away"). Thanks.
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