I have 1997 850 NA with 134K. For the past 1000 miles it has been using about 1 cup of coolant per 100 miles. I can find no coolant leaks however there is a gray foam on the dipstick when I remove it. The oil appears normal when I changed the oil, no milkyness. The oil filler cap and oil fill area look completely normal. The car runs perfectly, no white smoke from the exhaust. As far as I know the car has not been overheated although I am the 3rd owner. I assume this is a head gasket leak allowing coolant in tiny amouts to enter the crankcase. Has anyone had a similiar experience and how much risk am I putting the engine in by continuing to run it if it doesn't worsen. Thanks much.