Baddog,
When I had my X boat, I found it easier to wet sand the black part first, before rubbing out or polishing.
Use #1500 and put a little dish soap in a bucket of warm water. Use a sanding block and don't let the area dry out as you sand. Rinse with garden hose as you go.
Now, when you polish it out (as others suggest... machine works best), it will take less work and time and it will shine better than ever, when you're done.
I prefer wax for final treatment and have had great results with Meguiar's cleaner wax paste.
After doing this, the black areas seem to be easier to take care of overall. (just re-wax as needed)
As far as the WD40 goes, I've seen many boaters use it right after pulling their boats out of the water. First thing they do is get out the ShamWow , the WD and go over the entire hull. Also have seen many use Pledge. (yep, regular old Pledge... I used to see hot rodders and custom car guys use this all the time too).
However!!! Do mind the warning and don't get either of these products on any surface you may walk on. It will be like wearing Teflon shoes and trying to walk on ice
Best Breezes,
Steve K.
Mac 26D "Three Sheets"