ignition coil exploded

The problem is you had a constant 12 volts to the coil. Key on is to be 8 volts . Key cranking is to be 12 volts. when you were letting out of the crank position it was staying on 12 crank and fliping back to 12 run . you could have spiked it from a series of two overlapping 12's. The ignition if worked slow can sometimes operate two circuits at one time. You should always run a balast on oil filled coils to prevent this over heating from to much voltage. you probably had a jumper box or charger on it also. The oil shouldn't have damaged the paint unless it hit it hot. Properly wire a ballast for run only . It should be bypast for crank. Steve