All last winter I had to fill the overflow tank in my son's 1992 740 twice a week. This was right after he overheated it. Since the overheat was caused by leaking hoses I hoped against hope it was a leak. I looked every where for a cooling system leak but could not find anything. No antifreeze in the oil. Two weeks ago however I noticed oil in the over flow tank. So now I'm pretty sure its a head gasket. I have found a 1990 740 with a little less miles that has a good drive train (Drivable). I believe the engines will swap with no problem but does anyone think otherwise or something I should check on the 1990 before I buy it? thanks