Your story reminds me of my not so distant past
I started out in cnc with a Bandit cnc on a lathe and a Bandit cnc on a Wells Index mill. Typically, the control would run okay for a month or so at a time, and then it would get flaky, or quit working altogether. Lots of pin connectors to keep clean, lots of boards to keep pulling and reseating so the contacts made good.
I upgraded the mill 10 years ago, with a Shadow cnc, which is a spin-off of the Bandit, but still has only 10K lines of memory, compared to the Bandit's 1k. The Shadow was kind of designed around the concept that devoted Bandit users would want to be able to run exactly the same style code after their retro to the newer control.
If you have the correct RS232 port installed, either the Bandit or the Shadow will execute from a remote PC. The processing time is slow, though, so heavy 3d programs tend to run a bit slow, as the control cannot process segments fast enough to keep the feedrate up.
On my Wells Index, servo motors were used, even with the Bandit. However, the Bandit used tach resolver feedback, whereas the Shadow uses more modern encoder feedback. If you look inside your Bandit, I think its the 4th card in the cage that is named "resolver logic" and it will have a little piggyback card on it.
You can contact Control Solutions in Bozeman, MT, or the affiliate, Albright's CNC Support Service, for more info on the Shadow, and also some repair parts for Bandits. Also in Bozeman area, Wendland Browning Services offers some Bandit repair service.
I upgraded the lathe to a PC based cnc using Camsoft and Galil card. Actually, I went with new servo amps, the PC and Galil motion card, used a few buttons from the old cabinet. I used the original motors in it, but upgraded the encoders. Going this way considerably reduced the amount of wires in the cabinet.
PC is very nice, but its not cheap, the way I did it. Camsoft CNC professional was $5k, Galil card and stuff $2.5K, encoders and amps, another 1.5K. Plus, many hours of work to redo the wiring and create the user interface within the Camsoft framework.
Its nice to have all your program storage right there at your machine, with an optional cadcam also available right on the PC at that machine. I don't use the Camsoft cad system, but any gcode file can be created in any cadcam and then run right there, anyways.
I'd guess you'd have to spend between $7500 to $10,000 whichever way you'd want to go.
It can be such a pain trying to use old motors and drives with unknown specs, that its sometimes just better to toss and replace with new stuff that someone can service, if you need it. Actually, most newer electronics is pretty reliable, so that takes care of a lot of the headaches that went along with the old technology that used so may discrete components.