2009 Forester Automatic
I've recently had the heads, head gaskets, and valve cover gaskets, along with a few other parts replaced. Before the work was done, I would use about 2 quarts of oil between oil changes. Now, it's using 1 quart every 800-1000 miles. The engine shows no signs of leakage, but my chrome exhaust tips are black, so it's obviously going into the combustion chamber. I'm assuming it's the rings. Is there anything else that could cause this, like the pcv valve?