I have a 1980 633csi... I just change the oil on the correct mileage, check all the necessary fluids, and let it warm up a lot on cold mornings. The best thing you can do is baby it. Just listen to the engine, if it sounds weird, check it yourself, if you can't do that, take it to a dealer or service center. But if the M6 is anything like my car, it won't give you many problems.