Ok, so story is as follows.
A few weeks back, we had a Accord Type R come in with a horrendous noise from the engine. We instantly diagnosed it as a failed auto tensioner, (at this time my master tech was adamant these never fail
). He then told us that it was replaced around 14k ago/2 years. To cut a long story short, it was evident that's it was not replaced and infact, the garage that did the work ripped they guy off 
So we got on with the job of replacing it, along with new belts ect. I took the time today to actually see what part of the tensioner failed. So I will run through some pics. . . . . .
So here is the tensioner. I started by taking off the cap along with its boot. . . . .
That uncovers this . . . . . The retaining plate that is held in with a snap ring . . .
Just to add, this tensioner had completely failed, the adjusting shaft was floppy
. . . . . 
Remove the snap ring . . . . .
Pull out the adjuster shaft assy . . . .
Then inside the body I found the route cause of why these tensioners fail . . . .
This spring is wound against tension when it is set, then set to a pre determined setting at the factory. Then when you pull the retaining bracket off, the tension of the spring will equalize with the tension of the cam belt by spinning the adjuster shaft on a thread. We decided that this is the only way these can fail IMO, even when they loose there oil it should still function, (this still was full of oil). This is the cause of fatigue of the spring, failure then no retention of the adjuster shaft.
All the parts together . . . .
Thought it might interest you guys as to the inner workings/failure reasons for this part.
Cheers
. In my honest opinion, these should not be re used. The way I see it, is that the spring is under tension for the period of time it is, heat, vibration ect. Then it's undone when you take it off, then wound back up to re tension the belt, all in all weakening the spring 
But that's my opinion 
