I had missed that; in no small part because the notion seemed so ludicrous.
However in looking at the 119.982 my '98 500 it would seem to be the case--which I will call a complete half-asséd engineering feat--unfortunately not all that unique on these vehicles.
The crank pulley is so large in diameter that it does indeed look as though it needs to come off to pull the pump--completely absurd, in 55+ years of turning my own wrenches I have never seen such BS!
The good news is that the crank pulley has lightening slots and a universal crank pulley holding tool such as this should be able to hold it while loosening and tightening the bolt. The tool on eBay is a clone of an OTC tool, I have had one for years.
Use the appropriate set of extensions to fit into the slots on the pulley and brace it off to the floor as needed for loosening or tightening--use a piece of pipe as an extension if needed.
Note: As "expensive" as buying the crank holding tool might seem I would do so in a minute before letting some other "mechanic" screw with the crank bolt. There are far too many "I don't need no stinkin' torque wrench" and "guttin' tight" a-holes running around out there--both "indies" and MB certified. If the crank bolt comes loose and the crank nose is messed up that $120 is going to seem pretty cheap.
At least make sure the shop has such a tool before letting them mess with your car.
The spec for the bolt is an initial torque of 200 Nm (148 lb·ft; + an additional 90°; which is probably very close to 400 Nm. Almost any 1/2" drive torque wrench will get you to 200 Nm, a 25" breaker bar¹ and the holding tool braced to the floor will get the other 90°...
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¹ - It will take 153 pounds of grunt on the end of that 25" bar to get to 400 Nm--but that's not all that too bad--put a pipe on it too.
