My 90 560SEL has one... and I think my 86 560SEL parts car does too.

Perhaps this only applies to the six cylinder? My 89 300TE didn't have one.
I know our 95 does, just had to replace it.

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