x2

The bolt is just a standard metric cap screw. I forget which threads, but you could get one from boltdepot.com. Get a high grade one and use anti-seize -- I think the OEM ones have some sort of fancy coating...

Bolt
 

The bolt is M10 1.5 45mm long. I could not fit any 8mm hex wrench in there myself they would not fit needed about 1/2" cut off to fit.

Interesting. My w124 with the 603 was tough, but I got a hex key in there.

I have a made in china allen wrench set, titan branded I think, the 8mm key fits the bolt and clears the radiator fins too (best use a pizza box to save those fins)

I use the key to just crack it loose - my pulley holder is a water pump pliers which I use to hold the water pump pulley with belt on it.

After its loose I use the shorty socket to remove the bolt. You can buy this bolt from ace hardware if you want. You might need to polish off the sides of the new bolt head if its not a MB purchase.

treetops,

I got mine at Fastnal they are M10 1.5 45mm long. The ones I got were 8mm hex head. You can probably buy different heads.