Quoted from Homepin:

Yes, they say to replace them in WMS machines but the fact is they are almost always NOT faulty in any case. People will quote that the expected life of the caps has been exceeded blah blah blah, so what, the simple fact is that (in most cases) they are still working perfectly well and (usually) more damage is done to the WMS power driver board by people attempting to replace these caps and pulling the through hole "vias" out than any benefits gained by replacing the caps.
Have a look at the schematic for your machine and determine exactly where the supply for the GI comes from. Is is DC or AC? If DC, where are the bridge rectifiers that it comes from? Take measurements and compare with the schematic. What connectors are in line? Connectors are usually the weakest link in pinball machines. Are the fuses old and crusty? Maybe your problem is as simple as a fuse that has gone slightly high resistance and so is dropping a bit of the supply voltage - measuring will tell you this instantly.
Please don't just blindly shotgun repair the machine because you won't learn anything that way, you will probably replace a lot of parts that are perfectly serviceable and you might introduce additional faults that are not there currently.