My daughters smart, the Canada 1 BRABUS, was in a collision in 2020 when my son was driving and the left side headlight was damaged and replaced with a used one from a wrecked 2005 smart that had been in the sun for too long (crazed yellowed lens). So not long after she got the car and it was being stored outside as it is now, the light began to leak in the rain.
We had spare minty lenses and today we changed it. The shocking thing is that four of the 7 plastic clips that hold the lens on - the ones on the top of the car - had basically turned to microplastic dust and there was no recovering them. So: what to do?
Answer: make my own clips out of thick wire.
The rubber gasket was coated lightly with clear silicone and the lens was temporarily clamped to the tight position and then wire was tied over the lens clips and then they were tied tight and the vice-grips released. After wiring, the lens-to-housing gap was filled with clear silicone too.
The end result was satisfactory: