1999 Cadillac El Dorado Bad head gasket without overheating

When the oil level light comes on, it is approximately two quarts low. The oil capacity is 7.5 quarts with filter change. If this is an ETC it probably has heavy duty cooling and therefore, an oil cooler in the radiator(lines going to RH(passenger) radiator side tank. If this oil cooler leaks, it could introduce oil in the cooling system. If you had a blown, or leaking head gasket, you would more than likely see some coolant consumption, you make no mention of that. These engines also consume some oil, 1 quart in 1000 miles is considered normal, but it can be more than that in certain circumstances. I would recommend proceeding in this manner. Make certain that the oil is at the full line for reference, and also record the mileage. Drive and either monitor oil level periodically(every 1000 miles) or, drive until check oil level comes on. Compare with the miles and determine a more accurate rate of consumption. Certainly, oil in the cooling system is not normal, but there are possibilities as to why it is there. If your oil consumption is out of normal rate, and you see no change in the cooling system, I would recommend a piston/ring cleaning with top engine cleaner. Before I would consider a head gasket at fault, I would have a block test performed. If you have oil leaking past the head gasket, you would most certainly have coolant leaking in and/or hydrocarbons in the cooling system. Oil is only under pressure at one area of each bank of cylinders, that is the feed passages to the cylinder heads, coolant is under pressure(when under pressure) throughout the head mating area.