Coolant drip on oil pan?

I just changed the ATF in my '96, and noticed there was a drip of coolant just below the oil drain bolt on the oil pan. Couldn't tell where it had come from. Anyone have any idea where it might have come out? I have a small drip from the radiator drain, but it seems highly unlikely anything that drips there would end up on the oil pan...

Start hunting, worst case, the freeze plug in the back of the motor is leaking. It is on the back of the block under the flywheel. Might want to stick some dye in the cooling system then use a black light in the dark to do a look see.