All right, I found what it is. Apparently, an early JMI NGF-mini, the version for Newtonian telescopes. Still looking for a replacement eyepiece screw, but meanwhile there's another problem I've noted recently. At times, the motor would just not work; you press the buttons on the controller, nothing happens.
The behavior seems to be rather erratic, in the course of an observing session the focuser would work at first, then nothing for a while, then on again. I tried a different controller (I have a spare one), same same. After disengaging the motor, I found that the hand knob is very hard to turn, is it possible that the tension screw is just too tightened and the motor has a hard time turning it?
A JMI instructions sheet for a similar focuser I found online (http://www.physics.c.../ngfs_instr.pdf) stresses that everything else is factory tested and should never be touched, as pusher bearing alignment (for example) is extremely critical.
Edited by Quinnipiac Monster, 14 October 2019 - 05:18 PM.