I've tried a lot of things now so here's a list (more for my reference than anything)
- Changed condenser (no change)
- Changed points (and then changed back as the new ones were rubbish, but didn't alter the misfire anyway)
- Tried a different coil (didn't help)
- Made the mixture richer than normal (made things worse so I put it back)
- Made the mixture leaner than normal (didn't help so I put it back)
- Got rid of the points and condenser altogether by fitting a magnetronic system. This also meant fitting an entirely new distributor (still no change to the misfire)
- Changed the main HT lead from the coil to the distributor (no change)
I also drained the oil catch tank today and was somewhat alarmed when almost a litre of bronze coloured water (or what appeared to be water) came out along with the expected small amount of white frothy oil/water mixture. I can only assume that it was a years worth of condensation as I hadn't drained the tank for ages. There did seem to be rather a lot of it though and it was a strange colour. I'll have to keep an eye on the tank and see if it starts to build up again.
In between all this, and trying to do some overtime for work, I went to the Bronte Vintage Gathering which takes place not far from here. Spent a couple of hours viewing an assortment of classic cars, tractors, commercial vehicles and steam traction engines. Also the obligatory stalls, mostly selling tat. I bumped into Dave M there showing off his Triumph Dolomite. Only took the one picture but there was quite a lot going on around the field. Filled some time anyway.