Recently did the head gaskets in g/f's '07 Impreza. This is the normally aspirated 2.5L boxer motor, not the WRX turbo. Anyway, the oil and coolant leaks are now gone (bottom of the engine is bone dry after a 4,000 mile cross country trip from Florida) but it did use about 2 quarts of oil during that time. And before anyone asks, the PCV valve is brand new. So, even though Subaru calls for 5W-30 in this engine (I've been using Valvoline Max-Life 5W-30), does anyone think it would be worthwhile trying some Rotella T6 (or other XW-40) to try and slow down the consumption? Or is this a bad idea? The car is driven on a 30 mile round-trip commute at freeway speeds daily, and will be in the Seattle area, so maybe an occasional sub-freezing start-up, but nothing sub-zero.