It gets even better: here's the result of an 8-fob print:
The fobs were printed in the order numbered, takes about 32 minutes per fob. Fobs 1 and 2 are perfect. Fob 3 might be showing a little stringiness. Fob 4 looks horrible. Fob 5 was where I stopped things, because very little filament was being extruded. The clicking was virtually constant.
This was all in a single print job. Now, each fob does have its own process, but all the process settings are identical.
I've just spent a productive-- at least, that's what I tell myself-- half hour adjusting the tension screw, feeding in filament, retracting filament, and looking at the tooth marks. I started by tightening the screw one-half turn, which produced constant clicking when I pressed the "Extrude" button in Simplify3D's jog controls. I loosened the screw until this noise stopped, then went back a tiny bit further. I've settled on one-eighth of a turn looser than it was originally, and the tooth marks look good. We'll see how it goes.
(Of course, if it was a problem with the tension screw, how could it print for almost two hours straight before seeing a problem? Perhaps it was on the ragged edge of being too tight and the filament diameter increased a few hundredths, pushing things over the edge?)
((Thanks for the photo compliment. That's why people buy Micro Nikkor lenses. Love the newer versions with image stabilization built in.))
Oh, and PcS: the extruder has a month of what I'd call casual use. Maybe a hundred hours? And there's no spitting or other indication of water-logged PLA.