No idea on the plastic type, but if it were me I'd call a bluebird dealer with your Vin and get the part number, then search ebay for new old stock. Might be easier and cheaper to get a replacement than try to repair that one.
Unless of course, you're more into the adventure of the project... in which case, just tune me out
Edit - getting original part number may allow you to research it and get insight into the material from manufacturer?