The butyl tape or putty has been spreading out from the edge seams and turning black. I can trim some of it with a plastic knife, but anybody know what I could use to get the black off?
But don't substitute lacquer thinner or acetone! They will damage the surface.
I used fake acetone on my paint and it didn't hurt it (fake acetone being fingernail polish remover). It worked well removing sticky stuff. I'm sure real acetone is a different story. Mineral spirits worked too.