Problem(s) Encountered:

When I went to close the dropleaf at the end, I got a  slit busy  error and it wouldn't budge.  After a little thought I tried moving the dome to 60 degrees in the dome control panel window, and then homed it again, on the hunch that the contacts might be slightly off.  Whether that was the case or not, the dome closed normally.  (I inadvertently closed the slit first, being a bit flustered, and was obliged to open it back up before closing the dropout and finally closing the slit.)

Solution:

This likely was an early sign of a stronger problem that occurred some time later, where one of the contact terminals supplying power to the dome slit motor broke.  The terminal wiring has been fixed now.