I've been burning a quart or oil every 5k miles. I did not burn oil for the first 20k or so. I bring it to the dealer for maintenance, and they are using the 507 spec. I am also, though less frequently, running low on coolant. The car has 75k on it(mostly highway)and I've been thinking of switching to 5w-40 low ash, that's used on MB. But I guess my questions are, should I be concerned that she's burning oil at that rate? Is it a good idea to switch to a non 507 oil, that is low ash? Would any of this impair my ability to participate in the buy back? Would changing oils stop it from burning oil?