Thanks for the input. The car has 151,500 miles. There is a small puddle (the size of your palm at most) under the car after driving. I have watched the oil seaping from around the oil filter housing to block seal while the engine is running. As far as I can see there is no oil leaking at the head gasket. I know 1/2 a quart is not bad but I may be trying to sell the car soon (see thread in Diesel forum).