I am in the middle of changing the water pump on my 1993 300E. As I go about trying to order a new on, one on-line store just asked for my chassis...124....and my engine...3.2. They listed one choice for $129.00. Every other place, NAPA included, has two choices depending on engine production #. Oh ya, they all cost 60-70 dollars more. Where do I find the engine production #? Any ideas as to the differences?