I know this is an old thread, but hopefully this comment can help someone with similar isses.
I had the dreaded drawer failure to open problem. Research way back when said that the gear and drive pulley were no longer available from Theta (or elsewhere). I boxed up the unit, bought a replacement, and moved on. Since I’m an equipment hoarder, the unit sat unused in the closet.
Recently I came across the unit in the closet and decided to relook for the gear. Amazingly ebay had them from a seller in China, so I decided to take a chance and order one.
Disassembly was rather easy, save for some fiddley small screws. The drive mechanism is attached from underneath the base plate, so some gymnastics are required to release it without dropping it. One ribbon cable needs to be detached. A small circuit board on the bottom of the drive can then be detached (but not necessarily unplugged). The pulley, gear and small plate can the be slipped out. Remove the old pulley, clean the shaft, and slip on the replacement. The unit can then be reassembled, taking care to center the drawer in the faceplate cutout.
Unit now works great.
This is worth the effort, since this machine uses the Philips CDM9 Pro laser assembly. This mechanism is legendary, and is still being used in the new Jays Audio transport.
One other note - the seller from China does supply a replacement belt, but it’s the wrong size - hold on to the old one!