i guess my first question is what is exactly on that metal strip? meaning, is it water stains bird boop, etc.?
if it's water stains, use some vingar water 50/50 with tap water and spray at it for several minutes.
also try clay
also try some mild polish, but remember that the polish can stain the rubber strip around it.
you can Hydro it to keep it up.
on my car all i use is Griot's WindowCleaner these days just to wipe up any excess from cleaning the windows.