I've recently stripped down a 300 model and found the top bearing for the blade assembly worn/seized. It is an easy enough job to repair the only problem I had was removing the 'fan plate' that the blade sits on, owing to the fact that the aforementioned bearing was seized into place. Use a small scredriver or similar to RIP the ball earings out thus enabling the removal of the whole shaft.
Ian Ramsay, July 2005