I was riding with my friend on some trails, and what i think happened was a rock busted my chain tightener, its messed up pretty bad, i have a pic of it in my pics page as soon as it is aproved, its pretty nasty. and now it wont roll like it should, it kinda slugs now (wont roll fast). The outer gasket scraped some of it as you can see in the picture. can someone tell me how bad this could be? as in, how much am i looking at it costing, what am i replacing? etc. thanks for any help.

 

OMG, can someone please help me? arg.