My father recently bought a G37 at an auction. 2011, 30k. I pulled the dipstick, and it was low about .75qt. The oil was very black, and had a chunk of black gook on it! My heart sank a little, but I added a quart and am trying to figure how bad it could be. I put a flashlight down the oil fill hole, and things looked relatively clean. The engine idles quietly, and it doesn't smoke. Before you say "RETURN IT," he can't - it was an auction. What oil should I run in this thing? I was thinking Rotella T6 0w40, but maybe this is overkill. How about Mobil 5w30 Syn? Must this engine use synthetic? I did a search but 'g37' doesn't qualify as a search term.