I am sure I've commented on this before, it may be worth searching the archives...
Anyway, the normal problem, at least on the earlier drive, the one used in the 9114A, is that the grease on the eject mechanism goes sticky. The thing then doesn't latch properly when you eject a disk, the upper disk head gets caught in the disk, and gets ripped off the gimbal spring. If this has happened, you need a new head assembly, and you have all the fun of aligning it...
If the head is still OK, then you need to dismantle the drive and clean off the old grease. Remove the drive from the unit and take off any mounting brackets/plates. Undo the single screw on the back and take off the top cover.
Untangle the wiring to the stepper motor. Take out the 3 screws on the bottom and take off the screening cover. Ease the PCB away from the drive chassis and unplug all the connectors (note where they all go, of course). Put the PCB aside in an anti-static bag.
Inside the drive chassis (on the bottom, where the PCB came from), take out the 2 screws at the very front. Remove the front panel, don't damage the in-use LED or lose the eject button or spring.
On top, take off the eject damper at the back left (1 screw). Undo the 2 screws on the head load bracket (one holds the earthing tag in place), put a piece of clean tissue between the heads and remove the bracket. Feed the solenoid wires through the chassis and remove the complete assembly.
Underneath again, undo the 4 screws at the sides which hold the disk holder/eject mechanism in place. Remove the mechanism.
Take off the E-clips that hold it together. Pull out the shafts (don't lose the spacers). Unhook the springs (note where they all go). Then clean the old grease off with propan-2-ol (isopropanol).
Put it all back together, and it should be fine again.