At last something i can help with,what with being a fully skilled, top notch vehicle body repair tech(panel beater) no less .First 'V' out the cracks/splits,you can use a grinder,belt sander or 80grit rubing down paper,fold the paper use the edge of the fold.Rub/key up the area around the split with 80 grit.rub/key up the inside of the fairing with 80grit (the area behind the splits)then fiberglass the inside of the fairing,you wont need to rub down the fiberglass.Fill over the splits(outside) with body filler,rub down when dry with 120grit,use it on a rubbing down block keep the block flat on the fairing,repeat until perfect.When the shape is right rub down the filled aera with 400/600 grit(remove all the 80grit scratch marks)It will then be ready to prime .its as easy as that.If you dont fancy doing it go to your local car body shop and speak to a panel beater or painter,most of us who work on tin tops love bikes, most are only to willing to help a biker.Nearly all panel shops have a plastic welder or can do it the way i told you.If you do it yourself when you go to prime it get a can of high build primer and when you flat down the primer use 800grit and flat the whole fairing as well as the primer.Its now ready for top coat.As for Daves use of 4000grit(bless him),1 i didnt know they made 4000grit(you wont find that in any bodyshop)2 We flat with 1200 and up to 2000 on the top coat after painting just before its moped/polished.Hope its some help wayne.