If you have the oil pan off,pressurize the cooling system, and look up in the bottom of the crankcase at the cylinders. You will probably find one of the cylinder o-rings are leeking coolant, as the 92 series Detroit has o-rings on the cylinders.
I would advise you to change all the o-rings, if 1 is leeking, as they are dried out.When you reinstall the linners, and the head, go by the manual. IT IS CRITICAL, to get it right.
Steve N.