I have an older 4 tube fluorescent light (T12 blubs) with 2 magnetic ballasts. One ballast went bad and began leaking. I looked at the wiring on the socket ends and it appears that there is some interconnection but maybe that's just a tap wire for the parallel connection. My question is can I replace the bad ballast with a new electronic version or would that be incompatible with the remaining old magnetic ballast. Thanks.

The answer is no. Replace the ballast with the same ballast or replace the entire lamp assembly.

Personally, I would replace the light with an electronic ballast controlled lamps.

Electronic ballasts are quieter, deliver almost a 1 to 1 wattage. The lamps are smaller and last quite a bit longer.