Problem resolved!

In my first post I speculated -

If I had to guess, I think there might have been a burr or grain of sand in the articulated bearing.


Upon further examination by our club's Director of Maintenance (who also owns a PW-5), a burr or rough spot was found on both the interior surface of the articulated bearing and, to a smaller extent, on the tailplane pin.

A little TLC with fine grit wet / dry sandpaper and new grease did the trick. It now functions smoother than it ever has.