I had the chain, tensioner and ķpulleys replaced two weeks ago on my wifes tdi90. I was worried about the noise from the sump, at 105k worse than my tdi90 @237k. It turned put to be the idler pulley, the one with the the seven ball bearings making a rattle, the chain was rubbing against the crankcase but im not sure why(no pics from mechanic). The chain itself and tensioner were not bad so alot of labour for a ball bearing. Nice to know its ready for another 100k
On the photo the balancing pulley does seem to have pointy teeth, however i noticed the tensioner has pushed the chain up to the crankcase, so that must be a worn(longer chain). In my case it was only 2mm longer at about 35cm-impressive.
I suspect most of the failures may be down to a blocked oil supply to the back of the tensioner, which hydraulically pushes its arm against the chain. A slack chain would result which could get caught up on itself.