Mutt,

Are you referring to the spoiler below the bumper?

If so, there are two styles.

Early 450SL came with just the pan, no spoiler.

The 380SL had a black plastic flexible spoiler that fit below the pan and came around the side towards the front wheel opening.

The 86 and up cars had a solid ('glass, metal(?)) spoiler that covered the pan and had a rubber lip.

The black plastic style is flexible, and I would think it could conform to a W123 pan.

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