I decided to test the thermostat in my 1990 K75 while doing some other services. It passed fine, but the old gaskets could stand to be replaced. There are two: a special sized O-ring which seals the thermostat cover/retainer (which is available from BMW), and a grooved square-sided gasket which covers the edge of the thermostat "disk" and seals it in the thermostat housing (therefore it must be exactly the right dimensions). THAT gasket appears to only be available with a new thermostat ($55.00!!) according to the on-line BMW parts listings! Does anyone have a known source for a replacement thermostat body gasket? Thanks.