CJ wrote:bigjim wrote:... aluminium goes soft as it ages ...
Nonsense. What happens is aluminium corrodes/welds onto steel, with time, absence of corrosion inhibitors and exposure to dirty water. Eventually the strength of the bond exceeds the strength of the thread.
It helps to put a very light smear of Copaslip (or Alumslip is better if you can get it) onto the axle before fitting.
Shimano recommend that on all tapered crank arms