All of those double exposures I was getting on the Chinon were, I worked out today, due to a faulty winder. I sacrificed a film to watch how it wound on with the back open. After about 20 exposures the roll sticks. Then it moves, but soon sticks again. It's simply not reliable. It's a pity because The Old Man bought that camera new in the 70s, and it's like a member of the family.
So, as I can't afford a Leica - just yet - I'm going to get a Fed 2 off eBay, and probably a Jupiter 8 lens to go with it. A tenth or twentieth of the price of a Leica, and they can take good photos. And they're fun. And cool.