on my 260E 1988, I made a tool like the one described by the link mentioned by 5280BENZ, it is a rod 6mm diametre bended around 45 degrees lenght 300 mm on one side and 20/30 mm on the other. It is intended to block the rotation while unscreewing the central screw.
good luck

__________________
Keep us posted especially if your problem is solved
Present cars:
My car: E-class 420CDI, 2008, W211, V8, 180 000km

Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km

Son's one: GLK class, 220CDI, 2009, W204

Sold: E-class 260E, 1988, W124, Wonderfull car sold after 489 000 kilometres of reliable services (engine M103, clutch, brake system and 5 speed manual gear box all original).

Sold: E-class, 320CDI, W210, 2000, 225 000km