Thanks for your helpful advice.

I'm slightly unclear as to whether the screw adjuster mechanism is an integral part of the belt tensioner, and whether it requires removal along with the body of the tensioner. I would imagine I only have to remove the steering pump pulley, rather than the pump itself, to get at the third retaining bolt.

There's practically nothing in the Haynes manual and the MB CD-Roms don't cover the 2.3 W124.