Hi Max
Yes, a decade or so for general natural rubber products seems right.
I have seen how old rubber blisters and congeals over time.
When I started researching Pope Products I would always find
complimentary rubber garden hose advertising. It was the miracle
product of the day.
I guess the synthetic rubbers [Turner used Dupont rubber tyres] and
modern plastics offered much better stability and durability.
The 'Great Hose Mystery of 1955' must be sure fodder for
conspiracy theorists. I suspect communism as the root cause ...
It would be wonderful if a set of NOS fan blades would appear
for Champion or Villager mowers. That would solve the mystery -
rubber or leather. Maybe one day ...
Cheers and thanks Max!
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Jack