I recently bought LEGO Technic 8868 (Air Tech Claw Rig) and 8460 (Pneumatic Crane Truck) models. I noticed that the pneumatics tubes seem to have been changed since the colors are different from the instructions manual.
Since these models are respectively 24 and 21 years old, a possible explanation is that the original tubes have been lost.
But it may also be due to aged tubes that needed to be changed. How do tubes change when they're ageing? Do they become less flexible and break when they're failing? What is the lifespan of these tubes?
It looks like the pneumatic cylinder, pumps and valves have not been changed and they still work. So I think that they can last longer than tubes.