I've been using
Mothers Back-to-Black on my 1986 VW Cabriolet and 1995 F-150 for some time now. It does a good good bringing back the soft luster of the original black components on the vehicles. The truck's black plastic case on the exterior mirrors, rubber trim strips, etc. The Cabriolet has lots of black bits on the exterior so it's an on going exercise for me.
I just finished treating the R65s taillight housing with the
Mothers. There was a "shadow' from an old sticker of some sort plus the entire case was getting a bit gray... like some of us!
My favorite application technique is a one-inch wide disposable foam brush. Lay on the product fairly heavy (not dripping, but a full coat) and smooth it out as best as you can. Let it dry, then buff with a clean cotton towel. No streaks. Looks a lot better. Some components will benefit from a second application, depending on condition of the item. You may be able to see the difference compared to the un-treated turn signal housings.

You may notice I have shortened the chrome stalk with the turn signals on the ends. Reduced its width by about half or a bit less. Kind of tightens up the rear lights. I had been knocking into them as I was working on the bike. May do the same to the front if I work up the energy.