The workshop manual is pretty useless for this job as it lacks a lot of detail. In order to get to the blower motor on a gen 2 w126, you need to remove the knee protector/cover/thing which is held in pace by 4 philips screws and 2 plastic plugs. Three screws are hidden behind a small plastic trim piece as shown below.
And one more is accessed from underneath along with the two plastic plugs. To remove the plugs, in theory you should only need to turn them 90degrees and then pry out. But over time stiction sets in and its never that easy.
The fan cover is held in place with 3 or 4 screws. The two 10mm nuts do not need to be removed. They hold in the resistor. As you can see, my old fan is covered in dust and is likely what has caused it to seize.