Incidentally I talked to Newton Commercial about the seats, and they said nobody makes replacement springs/foam etc. for them any more. They could probably make me a new set of covers but they would cost about £260 EACH! I reckon if I manage to solve the comfort problem the next task is learning to make seat covers myself. Either that or get hold of a set of those furry elasticated covers that used to be popular in the 80's. :)
The replacement rotor arm turned out to be only a temporary cure for the misfiring. It started doing it again after the drive down to London, and got gradually worse last week. I've bought a new set of ignition components so I can try replacing a bit at a time to track down the source of the fault, but I decided to first try giving everything a good clean. There was a surprising amount of crud on the contacts in the distributor cap, and the plugs were sooty from all the short runs to and from work with the choke on for part of the journey.
If the rain holds off I'll adjust the brakes, grease the nipples, check the tyre pressures, etc. this afternoon.