For some closure, a new motor fixed it a treat! The owner is so pleased with it, apparently when it went she consigned it to a cupboard and bought a crappy vax upright, and used it for 2 years. She said she forgot how lovely her old one was to use!
Not often I get actual feedback on a machine, so I'm glad I stripped and washed the cyclone, washed the pre motor filter and fitted an air freshener for her now!