The M=B parts system has a bug so the dealer may give you the wrong pump. It happened to me recently with my son's C43. The C280 V-6 is not typically equipped with the oil cooler. The C43 with the V-8 is. The oil cooler is attached to the side of the oil filter housing. There are a pair of aluminum pipes that connect to the cooling system. there is a spud on the driver's side end of the water pump that connects to one of the pipes.

Like I said. it is unlikely you have the oil cooler.