Would like input on oil consumption. My 1990 325i has 93k mi. First 1500 mi after oil change w/ 10/40 Valvoline - no consumption. In ten days thereafter down a quart. Same thing happened last oil change, both times after oil level sensor came on. Does a slight reduction in level result in greater consumption? Does running at higher RPMs (4000-4500) have a meaningful effect? I show no signs of leakage or unusual exhaust smoke. Thanks.