REAR SHOCK
REAR shocks on early bikes can lose their damping. Some have been known to fail after as little as 5000 miles.
Even if the bike you are looking at has done less than this, which is very unlikely for the age, check that the shock is working properly.
Hold the back of the bike and pull it upright so the sidestand isn't touching the floor. Flick the stand up. Now push down on the rear seat and see how quickly it returns when you release the pressure. It should return at a controlled rate. If it springs back and then takes a little while to settle, the damping is shot and the shock needs to be replaced. A new shock will cost from £300.