Keith,
Knowing what is do about high voltage as an Radio Engineer, I would change out your coil. The secondary wiring (the one that produces the high voltage) generates a lot of heat. It's the oils job to transfer the heat to the metal shell of the coil case for cooling. The loss of oil from your coil is like the loss of coolant from your radiator, sooner or later it is going to overheat and leave you stranded.
Steve