Removed old tensioner pulley this evening, very simple, not a lot of room but enough to put a torx socket on the stud and a 15mm open end on the nut. Required very little torque; maybe too little (anyone know what it should be?). The bearing cage on the tensioner pulley had broke - glad I decided not to drive it today.

While there I tested the other pulleys and the idler was a little rough. Popped the plastic cover off the hub and undid the bolt. However the bolt is really long, too long to get past the fan; if MB in their wisdom had notched a fan blade it would be easy to pass. As it is I'll need to either remove the fan or leave the idler unchanged. I'm still surprised that they couldn't have worked it so that replacing the idler didn't require removing the fan - is there a way around this?

Peter