Have you been following the Mercedes Benz " SERVICE BOOKLET PASSENGER CARS " enclosed with the Owners Manual?

If you have been following the booklets service requirements then there really isn't anything demanded to be done at 100K.

have you ever had the transmission fluid changed?
when was the rubber accessory belt last changed?
when was the battery last checked?
when was air filter last changed?
when were the spark plugs changed?
when was the fuel filter changed?
when have you had brake work done and what was replaced?

It is a good idea to raise the car and inspect tie rods and drive shaft rubber boots for axles look for any leaking or rust also check brake line condition but that is really just regular mantenance and some dealers may have a special deal or mailing where they will fo this for free.

Nothing is really demanded at 100K if you've been replacing coolant and brake fluid at intervals

and for the 595 you stated unless a detailed list of what will be replaced and inspected and what the charge for inspection is. and then you additional charges if they find anything wrong and what the labor rate is.

why don't you answer the above questions and we can guide you on what if anything you should do.

I also own a 1998 C230