Overheating 300cd

[moconn]

Hi, earlier this year I bought an 82 300cd(my first mercedes)with 170K + on the odometer(not working). The car ran great for about 3 months until it overheated on a very warm summer day. I parked it and tried to find the problem. The Radiator had a cold spot at temp. so I put a new one in. This didn't solve the problem as after about 50 miles of driving on a cold day it got warm(hot) again so I parked it again. Yesterday I deciced to crank it up and see if I could spot something, I did. After letting it warm up a bit I pulled the oil fill cap and noticed steam coming out, not good. However there doesn't seem to be any water in the oil pan. What bothers me is the motor runs really good even when it was overheating. I don't know alot about mercedes diesels so I'm not sure what to do now . Is this a head gasket issue or a possible cracked head, is there a way to tell which without tearing the motor down? Or do I need to roll up my sleeves and tear off the top end(I am capable). Also if it's a cracked head are these heads repairable. I really like this car and would like to get it back on the road so any help would be much appreciated. Thanks Moconn.