Being my suggestion to buy another distributor I offered to check it out and give it a once over, and have ready to throw under the front seat for a rainy day.
As we know, when you have spares you don't need them, when you don't, well that's another story.
With these secondhand 635B's, as long as the bottom gear is ok, the rest is usually straight forward.
Pleased to say the gear was in perfect condition.
The inside was full of congealed grease and surface rust that was binding up the shaft and the auto advance mechanism.
The only way to fix this was a completed strip down, clean all the parts and remove any rust.
This photo below shows the amount of gunk that had collected inside the main body, but surprisingly it was only skin deep, and was easily removed with a small rotary wire brush on a dremel
The outside was then cleaned ready for a coat of high gloss black paint
The original points were in very good condition, and after cleaning up the contacts they were re-fitted with 25 thou clearance, a dab of grease on the cam. This was followed with a good second hand rotor button.
The grease cup was filled, the shaft was lubricated, and the final step was a distributor cap.
This little baby is ready to throw under the seat, hopefully never to be used. But if needed it will drop straight in.