Only MB could make a car that uses model specific parts.
Where it would of made more sense to use one from a sedan they had to design one that only fits that car.
And, because you need it to drive your car so you can have signal lights, this becomes a safety issue.
I see this far too often on other MB models. Mechanical parts are not too bad but on certain trim and safety items, forget it. 230SL production is about 70% of 190SL production and you can get almost anything for a 190SL. I guess the value of a restored car is the determining factor.