When I bought my first Amazon, back in 1959, I asked the dealer what part he thought might fail first. He said, "timIng gear", and I bought a spare because I was taking the car where service was not readily available. I carried that gear in the trunk of two Amazons for 25 years, and it was still there when I sold the second one with well over 150K miles on the clock.
They give you ample warning when they start to go, and they are fairly easy to replace without pulling the engine. If I had a new one in an engine, I wouldn't change it on the chance that it could break down ten or more years from now.
Bob S.