The last 2 times I had my oil changed the check oil level message has appeared on my dash. My STS only has 54k on it and the message appears way before the 3k window is up. Heres my question. I know it calls for 7.5 quarts of oil and will take up to 8, should I insist on the extra half quart or is there possibly another looming problem? Has anyone else had this happen?