my best advice is to ensure that ALL of the cooling fans are running up to spec.
if i were you i would just replace all the cooling fans with good quality ones.
the ambient temperature will also affect the electronics life as well 68 - 70 degrees F is recommended for electronics.
of course your incoming 3 phase needs to be somewhat clean also.....
it should be be within 10 - 15 percent of the rated voltage....all the time......(now this is quite hard to do without local regulation....)
for normal use the electronics will last 20 - 50 years or more......as long as they are kept within proper operating temperature.
replacing the spark cables might not be a bad idea if they are rotted and cracked due to edm oil. (they get hard and brittle down in the tank)
i reccomend running new ones all the way from the generator rather than cutting off the bad stuff and splicing in new wire. (splicing may cause weird impeadance problems at certain frequencies)
long duration dead shorts of the electrode/workpiece should be avoided, although most machines will detect and comp for that situation....however yours is probably a manual (non cnc) machine which
may continue running during most shorted conditions...
the Z motor driver is usually the circuit that fails in that type of machine....
hope some of this helps.