Hmm..... I just read the complete thread. I realise the previous errors I made. I had some cheap Shimano Chains, and they would only last a few thousand miles. I rode the bike along a beach and that (same as all the others) chain only lasted 300 miles. I tried using one of those 'whirling brush' gadgets with a solvent bath that clips on the chainstay and the drivetrain is rotated to clean it - worst decision ever! I suspect it was almost impossible to get all the solvent out from the inside of the chain- even drying 24 hours and then lubing gave the chain about 1000 miles life. My recollection from earlier years (20 years earlier) was that drivetrains and chains in particular lasted a long while, and indeed I was probably doing 12k miles a year commuting etc. This made me think that the chains I was using now were inferior. I changed to a more expensive chain KMC X8.93 and the chains last a lot longer. My regime (as always) is to keep a regular check on the chain cleanliness and measure the length with a steel rule and discard the chain before 0.75% wear. Cleaning....... remove chain, put into jar containing paraffin, and aggitate a few times over the next couple of hours. hang chain to dry for a couple of hours and squirt it liberally with TF2 spray - remove excess with a clean cloth and refit to bike. Seems to work. My belief (and it is only that) is the hardening of the chain parts is the most critical thing (all other care being done). I wonder if e-bike chain (which by definition is more durable?) is the thing to use. I've just lookes at KMC and it seem s ebike chains are for 10 speed or more. I shall investigate further o see if I can find 7/8 speed ones.