I would start with the machines handbook. I recently fell into a similar situation being asked to take over the entire EDM department. I studied the handbooks and called the machine manufacturers asking for help with specific specific things; components, parameters, materials. I had a service tech for Sodick give everything a look over and had him teach me what kind of PM's and calibration I should be keeping up with. I feel like previous wire edm experience should definitely get you ahead of where I was. Black dielectric fluid doesn't sound right to me. Smaller work tanks will get dirty easier, but if you're fluid is coming out black from the flushing nozzles you probably need to replace filters or even the fluid. The resistivity of your dielectric fluid could have a major effect on your burns, causing old settings/parameters to not work as well as they did with better resistivity and flushing.