Well, I've pretty much determined that it's internal. TO bearing or the pivot on the fork or something (would this truck have that pivot ball on the fork like the OBS/ZF does?). I had the shifter boot out, and when I operate the pedal, I get a distinct squeak near the bottom of the travel, coming from the bell housing. And as I release the pedal I get the slightest bit of sticking. Not enough to keep it from working, just that it's not silky smooth. I noticed a couple of visual access holes in the bell housing on top, you can see the PP from the cab through those holes. I can't help but wonder if there's a way to get some lube in/on the shaft and/or TO and/or that pivot, reaching in with a tool through those holes. Don't think I want to spray anything in there; I wouldn't want to get it on the clutch faces. Anybody ever tried anything like that?
Oh, that hydraulic line is actually more rigid than it first appeared. So that was a (bad pun) red herring...