Problem(s) Encountered:

The big one is was at the end. I went to do a standard star near the zenith and the dec stuck near 15 degrees -- I couldn't budge it with the paddle. So I turned off the drive, or so I thought, and figured I'd close at that position. But the mirror cover would not close. I went out into the dome to investigate, and the telescope started slewing north. I managed to stop it using the software "stop" sign on the TCS control program, but then -- I found the telescope was *under the pole*, and alternating between slewing south (toward the N horizon) and then moving north (up) more slowly. Meanwhile I had tried the mirror cover and it closed, WAY to the north, but on the meridian, undoubtedly out of order. I finally went in the computer room and powered off the motor controller chassis, just to keep the telescope safe.  
It is now pointing far north, under the pole, and I can't get at the dewar or the dark hatch. I did home the dome earlier in the process and so was able to close up. Dewar was filled around sunset.
Before that, the dec problem described earlier occurred, with a new wrinkle -- after some minutes of guiding, typically, the dec motion would freeze, so the star would drift along the slit. When this happened the dec would not respond to set or guide paddle input.
If it should matter, when the dec jumps described earlier occurred, the encoders did follow along faithfully. They appear to be about a minute of arc. The dec will behave normally until it hits a critical dec, then jump at the next correction. It's as if there's a dead zone (or the opposite) which gets jumped across. 

Solution:

Noticed “dead spots” where the motor would not respond to commands to move.  A light ‘bump’ on the drive train would ultimately result in motion, but this problem occurred numerous times.  Swapped out the motor, resolving the issue.  As for the failed motor, I am consulting with a few vendors in an attempt to get a replacement (or two).  These motors however are no longer manufactured and I am having little luck finding equivalents that would work and accommodate our onboard encoders.  Hopefully something turns up.In addition, I suspect the problem is actually with the brushes for the motor.  Replacements are available and once acquired, I’ll test out the motor with new brushes.