Is it a TD5 disco John? My son has a series one disco V8 and would not get rid of it for anything. Not over fussed on diesels myself. If it is a TD5 then would be looking at trading it in as soon as possible before you are up for big bickies for electrics. As for changing discs they are quiet easy to do and they have the minimum sizes stamped on the edge of them so you can measure them yourself to see if there is any wear.
That's the way the mop flops.
My thanks to Brian for this site.