while I was searching for bumper repairs, I found this one:

How to use the PlastiFix Taillight Repair kit to make permanent, nearly invisible repairs to your taillights.
http://www.urethanesupply.com/repairtaillights.php

they have more good info such as:

How-To...
Identify Plastics
Repair Plastics
Fix Bumpers
Use PlastiFix
Use Bumper & Cladding Coat
Use Bumper & Cladding Adhesion Primer
Remove Wax From Textured Plastic
Restore Cloudy Yellow Headlights
Repair Aircraft Parts
Repair Kayaks and Canoes