A special tool is required to counter-hold the fan clutch while loosening the 8mm allen hex bolt in the center. The part number for this tool is 103 589 00 40 00.
Removal
Remove fan shroud
Rotate fan with the 8mm allen hex bolt to align the counter-hold tool into a retaining hole behind the pulley.
While applying pressure on the counter-hold tool, loosen the 8mm hex allen bolt