Thermoplatic Fender Repairs
 

Can these fenders be repaired? On the expressway a truck unloaded his gravel and one of the stones hit the plastic fender, right below the lights. It cracked across and lost some paint. All pieces are intact, just a crack.

Not sure what type of plastic the BMW fender is made of, but there is a technique called "Plastic welding" that is used to repair motorcycle body parts (lots of plastic body parts and lots of opportunities to break them):

EmpireGP.com - Motorcycle Plastic Welding, Gas Tank Repair, Custom Painting, Race Replicas

50 Piece Plastic Welding Rods


Search for a body repair shop in your area that claims to be experienced with plastic welding and let them see the damage, As with metal welding, or even more so, experience is the key to a good repair.

Attached is a pix

If they can access the crack from the back, they can probably repair it. Again. hard to say not knowing the type of plastic, but the repairs I have seen involve making a "V" shaped depression on the back of the crack and "welding" with plastic. This should provide structural integrity anf prevent further deterioration/spreading of the crack. It's then a decision of whether to go further to finish and repaint the front side, or live with the crack in the paint.