When I changed out the water pump on my 87 300E ten years ago, I recall this question.

I *think* the explanation was that the water pump had changed at some point, and if you had the early one, you needed this part to adapt the later style.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles