Sid, I recommend that you have a local independent mechanic with MB experience evaluate your engine noise. The mechanic should be able to determine the source of the noise and advise if the engine needs immediate repairs or if continued use of synthetic oil will gradually eliminate sludge build-up in the valve train. Otherwise you're rolling the dice and continuing to drive the car in its current condition could result in more damage and added repair expense. The previous owner may have been apprised of an impending huge repair bill and decided to sell the car instead.

__________________
Fred Hoelzle