Good call Alan
Tensioner being replaced but that could be a clue to the initial fault.
A week before I bought the Bongo, Oct 2007, the cambelt was (allegedly) replaced but no mention of tensioner being done too. (Previous owner had problems previously & bodged it on a budget to flog it on

)
There had been a very subtle click-click-clicking sound, increasing with RPM over the previous couple of weeks, almost inaudible but you notice these things on your own beast after a year or two.
That may well have been a sign.