The cover is broken, the thing still on but doesn't look very trustworthy. Is there aftermarket or alternatively fitting parts from other models? Mine is a 2001. Google wasn't of much help sofar
All the parts you might need are on this page - http://totallyttrs.com/epages/699105d9-e4cc-4b32-b236-84e72cd67f84.sf/en_GB/?ObjectPath=/Shops/699105d9-e4cc-4b32-b236-84e72cd67f84/Categories/Shop/Chain__Sprockets
It includes an after-market aluminium section that is perfect for what you need