Did a quick search here for tips on adjusting the flower nut, and reassembled everything. There were a couple of identifiable shavings of clutch puck in the gritty crud in the bottom of the case. A few adjustments and it's good to go, started up and scared the crap out of some of the local skate rats. So, looks like I'm probably going to have to replace the set of pucks, not something I'm looking forward to but doesn't look that complicated (now).
So I'd say nothing wrong with the piston or jug (this time), looks mostly like uneven wear on the clutch pucks. you can see the wear on the back side of the clutch plate on one of the earlier photos. I'm thinking the odd noise was the sound of the loose puck shifting from one edge to the other of it's hole, or shifting and binding against the clutch plate when it was disengaged.
Of the replacements offered by the sponsors on the sidebars, can anyone recommend a better set? I know anything other than the factory set is better by default, but beyond that?
Thanks again for your ideas and help. I'm back up and running again (for now).