I have used a product called "3M Citrus Base C!eaner" works very well on any grease,oil ,silicone and the dreaded black streaks. I have used it on custom cars and aircraft,even over decals. Won't damage fiberglass, gelcoat paint. I went over out new TT after bringing it home and found silicon smuges all over and worked fast and easy.
2015 GMC Denali HD ,Duramax with Allison trans. 2500
2014 Rockwood Signature Ultra Light Diamond pkg 8315BSS.