you might be able to just replace the cas cover and be good. Sounds like the cover did its job, took the brunt of the hit.
You could run the motor without a cover to see if it was working, then just buy a replacement cover. I think there are clear ones out there. Frsport has an aluminum one
http://www.frsport.com/Circuit....html
I believe the cas units are all the same for s13, s14, s15