Thanks very much for the detailed info. A few points:
1. Before starting, press the two buttons in on the bonnet locking clips which allows the bonnet to go vertical, avoiding a banged head & makes access much easier.
2. I couldn't find my allen keys so I did not remove the wiper arm, but no problem to remover the w/s wiper assembly provided the blade is parked.
3. When removing the grill, the bottom two screws are a bit tricky to find being screwed vertically onto the chassis, whereas the others are horizontal. They are below the two big plastic screws.
4.I replaced my W124 fan from a Biehr type installation with a Bosch type fan/motor from a W 190 - No problem to fit, the blades are slightly smaller dia, and have to be tapped in to make the spacing the same,but much easier than swopping blades from the old motor. Just use a socket on the bottom end of the fan & other socket on the to end, with the fan standing vertically on the bench & tap the top socket with a hammer till the spacing is right ( 112mm inside edges or 238mm outside edges)
The airflowfrom the fan on high speed is fine, maybe slightly less than the correct fan, but fine for me. I sprayed the bearings with WD40 before re-installing.
On the Bosch Motor the brushes are accessible for replacement but on the SM motor ( MS 120-01-82) used on the Bheir fan, the motor is in two halves rivetted together, which would have to be drilled out to change the brushes.
Also the Bosch Motor is slightly smaller diameter so you need to pack some double sided foam pads around the motor body so that the clamp is tight (probably makes it run quieter)