Use a Product called "Y10 cleaning gel" its only slightly abrashive to give the chemicals in it a start, and I'd swear by it. It is rare that I would say that it is worth paying the extra for a tub of something from a "Sindelry" but this is good stuff.
Using a rubbing compound is harsh and as has been said will only wear away the couple of mil. gel you have already, so eventually abrading it will no longer be an option. Once its clean, polish it up and wax it with an ant UV wax, this will protect the area and act as a preventative maintenance (the most economice type of maintenance!)
I'll stop banging on about it now, honest I'm not on commision but its good stuff!.