I thought she was safe at home!

[DP1400]

By their very nature, shaped `plastics` if cracked, will always want to ping back into their original shape, so what i`d do is carefully check the crack and ease out any material that`s preventing the crack from closing. In this case it`ll probably in the area of the mounting hole. Once cleared out, the crack will, likely as not, snap shut. Once you`ve achieved that, carefully ease open the crack again, just enough to run some Araldite into it. Then let go. Check the join is correctly aligned then immediately wipe away any surface glue, (otherwise you`ll never get it off!). Once set, the joint will hardly be noticeable.

[Kiwifruit]

Jambo you could work away quietly with a scalpel from the under side and carefully trim any burrs away letting the crack close.
There are some great plastic repair glues. Autobody repair suppliers may be a good place to try.
Good luck with the repair. 

[GSXKING]

Don't bother painting it either. I think Grog's mudguard is a carbon wrap and it looks the business 

[lawrie]

I made some from GRP, & incorporated the extenda-fenda in the mold so now I can make longer front fenders!