Hey finally you pull the trigger!!!
Good for you will enjoy it! I love the way swb W126's drive.
As far as the coolant tank don't worry about it unless the level is going down. I am extremly picky and anal about maintaince and even mine isn't filled exactly up. As long as their is coolant in the tank you are fine.
When you do change the plugs make sure to use the proper ones. Get the no resistor copper ones. I got a set for an S320 from the dealer for $2.50 each, the dealer was cheaper then the autopart stores!
