If it is a capacitor problem it's easily fixed. Armature replacements can still be found, they turn up now and then but not often. A local repair guy who bothers can likely do something. I thought the commutator only became damaged if the carbon brushes wasn't replaced? Armatures from the 1920s are still turning fine in many cases? Looks like the armature will cost nearly £70 when ordered from
an ebay seller in Australia (...of all places, it could not be further away). My 730 would be worth it. With a bit of patience something more local will turn up. I would as Helen Howes too, even if it isn't a treadle.