My 99 neon overheated last week. I got it back home and while checking it later, i opened the radiator cap and a coolant/oil mixture the consistency of a chocolate milkshake oozed out. I checked the oil and it was slightly below the full mark on the dipstick. The dipstick showed no indication of coolant in the oil and never has. Two days prior to overheating, i added a quart of oil. It has had a slow oil leak for a couple of months. The coolant, hoses, and thermostat were replaced in the fall of 2003. Is this a head gasket problem or something else?

Yes it is,The headgasket a common problem and that is the oil leak too.