I would add that on my 300SEL, the bottom screw for the distributor cap was tricky to get in and out. I ended up using a hex bit socket with a universal joint adapter. It would also help to have small hands and good direct lighting.
Another possibility would be to remove the fan blade for more access room, but I didn't take the time to figure out how that's done.
I seem to remember that the three screws take a 5mm hex bit.
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino