I know there are plenty of threads about belt tensioners but there is some advising to use aftermarket and some say to use genuine.
I am assuming mine is stuffed as I have a high pitch squeal coming from that area on idle that disappears when I accelerate so am planning to change it.

Who has changed one on a CRD and what did they use, genuine or aftermarket and where is the best place to buy?

Being mechanically challenged should I change it myself or leave it to a mechanic?