It is very uncommon for tensioners to "just die", they usually give warning signs such as noise. It's common to change parts during the course of a service that we can see as having a iminent failure but when questioned as to "why haven't I noticed" by the customer or "can I see the BROKEN parts" they find it hard to believe that even though it seems good now that it will fail shortly.

Most new tensioners will last a long time, but then again, so do the belts relative to the older v belt style.

Your tensioner may have been showing signs for a while, you might not have noticed them.

__________________
Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32