As I mentioned, my first failure was of cable of the original spec, that is galvanized wire spun over a naturel fibre core. Having stainless steel cables is therefore not original and the original spec is no longer available. It has been suggested that the ss case hardens with repeated flexing which could be a factor in the problem. Changing back to a galvanised cable even without the fibre core might be an option which I could try. I am also guessing that the blocks have been changed too. I changed two of them due to excessive wear.
Thanks again for the input, all welcome.