A machine of that vintage should be powered by a PC based system with ISA interface cards. The heart of the system is the BMDC machine controller card.
The same card and basic operating system (albeit specialized for the particular machine) was used in the VMC's (800's and 1000's), TorqCuts, Eztraks (2, 2.5 and 3D) , X2XT's (3D and 4D), Explorers, Ezpath lathes (3 models ) and Ezsurf surface grinders. The machine control program is running in a DOS 6.2 or 6.22 environment.
If you are DOS and PC conversant, you can pretty much and readily service the PC side of the machine yourself. It uses garden variety hardware (good and bad depending on how 'clean' they kept the cabinet insides). The BMDC side does need a good tech to tune the servos every so often as it does NOT have autotune capabities - it is a mid 90's system afterall.
I'm a fan of the basic control system. It is no frills and if it comes factory fit to run 4 axis, you should be in good shape.
I'd be sure to have the machine demonstrate an ability to run under power and run in 4D to cut air before I'd buy it - just to make sure there are no surprises when you get it home.
The machining quality is going to be a funtion of the wear in the machine. The controller is capable of easily holding tenths in accuracty and repeatability. The overall machine accuracy, however, is going to depend on whether or not the THE AXIS' DRIVES & SCREWS ARE IN GOOD SHAPE AND FREE OF WEAR AND EXCESSIVE SLOP. Naturally, servos that are tuned poorly won't hold squat for accuracy.
Hope this helps