If the Vinyl Care is leaving an uneven finish, or "fish eyeing", it could be that the area has been cleaned previously with a silicone based product. Our premium Vinyl Care is water based and you will need to clean the sill down with our Orange Agent citrus cleaner, or the Sublime Clean exterior cleaner.
If you have really dirty, muddy sills, it will pay to clean the dirtiest areas twice, using clean sections of the applicator pad or cloth each separate time so you're not rubbing dirt back into the cleaned areas.
The best effect of hiding the scuff marks will come from darker coloured door sills. It's a rare one to have white or tan plastic, but regardless it will still clean these up pretty well.