best way to stop those cracks running thru the fairing is drill a small hole say 1.5mm diameter at the end of the crack.the crack will not go past the hole.
fill the hole with body filler
on the inside of the faring where the crack is follow it along and put a small "V" in to it for glue to get in to it and bond it
i use a small tip on a dremmel tool the shape of a ^ and do it slowly or you will melt the fairing
then once the v is done get some sand paper and on the inside of the fairing again roughen up the surface for a centimeter to two back from the crack so the glue can have a good surface to bond to
and then go nuts with jb weld and fill the groove you cut and spread it out a bit to the parts you sandpapered
this will fix the crack permanently
i have lost count over the years the amount if fairing i have fixed like this and it never lets me down
http://www.jbweld.com/