All of those belts were changed just in the nick of time!
If you look on the outside face of the timing belt you'll see a shadowy image of where the pulley teeth have been. I call this "ghosting" - it's a technical term but only in my dictionary!
Joking aside, it only appears on belts that are getting close to the end of their lives. I think (from memory) the interval on the red-block is 36k miles or 3 years for the timing belts. The time is important as well as the belts themselves deteriorate like all rubber products and the fibre reinforcing inside also stretches/gets weak. I'll let you draw your own conclusions.
As for the tensioner, any roughness in them and change them! They can deteriorate rapidly to the point where they end up throwing the belt. Had that happen on a Mitsubishi about 15 years ago - the upside was it saved me from a weekend with the monster-in-law so it was all good!
