Having previously bought a new rear hose and Angus's book from them I just got new filters from Manchester Vacs (brilliant high speed service) and fitted them using the advice in Angus's book for the post motor HEPA one. The original 6 year old HEPA filter was very black and dirty.
What a difference this has made, I'd forgotten just how good this machine was when it was new. The animal head on the hose now spins all the time without stalling.
As young people say nowadays - RESULT!!