Clutch woes with 93 Tercel

I own a 1993 Toyota Tercel 4 cyl. 4 speed with 77,000 miles on it. 3 months ago I had the clutch replaced because it gave out while driving, $800 down the drain. Recently, I started having problems shifting gears. Sometimes the gears shift seamlessly, like cutting through butter, other times they do not budge without repeated clunch pumping.
I brought the car to my usual mechanic, who said the clutch needed an adjustment. He supposely adjusted it, but the problems persisted. He told me that being the case that the clutch needed to come off and be replaced again (different mechanic than the one that replaced clutch).
I told this to my neighbor, a retired mechanic who offered to work on the car at a very low rate. First, he bled the system to make sure there was no air. This improved things for a few hours, then the car starting having horrible problems shifting. Next he replaced he slave cylinder. Again, it worked well for an hour or so, then back to the same old problems. Now he says it must be the master cylinder. He also tells me that it's nonsense that the previous mechanic adjusted anything, saying my clutch is not adjustable.

What I'd like to know is:
1) is there any chance this is a fundamental issue with the clutch itself, not the cylinders, and that I should be taking this up with the place that replaced my clutch?
2) is the latest guy right that my clutch is not adjustable, and that it makes no sense for mechanic #2 to have claimed to have made an adjustment?
3) do you think that replacing the master cylinder will resolve the issue of sometimes having trouble shifting, other times not? I seem to be able to drive fine for a while, then have the problem many times in a row.

Thanks so much for your assistance with all this.

-Banterman