On my 89 240 I painted the faded cladding with SEM black trim paint. My side plastic was really light grey but when I purchased the piece that wraps under the bumper it OE color was a darker grey. I washed it all with dawn, then sanded the pieces very lightly and then painted. Note all the parts were off the car when painted.

You can see on my black car how light grey that one looks. It too will be black soon.

Silver could go either way: both grey and black will look good.

Alcohol based cleaners seem to work well for removing silicone, as well ammonia, but I would look for a specific product or the purpose; I'm sure they exist. If you are painting anyway, you may want to wet sand with hot water and detergent, or use another fine abrasive like scotchbrite grey.

SEM makes the best products in an aerosol can I have ever seen. They cost more than the other guys for a reason. Also, if you ever want tips on using any SEM product, give them a call; I guarantee a friendly voice will tell you everything you ever wanted to know about how to get the best results.