It's not always just the oil's weight that affects the operation. I'd suggest draining the Amsoil out and refilling with Extra-S. See how that goes, it has worked for more than a few people. Motul is another that gets good comments but may not work in every case. Extra-S is slightly cheaper than Motul so why not? There are vendors taht sell Extra-S by the quart instead of the Subaru "mighty" pail.