which market/country are you in that the car is a C240?

Contact Mercedes and get a SERVICE BOOKLET and OWNERS MANUAL.

You may also contact your local dealer to see if the car had been dealer maintained and if so what work has been done.

The 90K mile serivce is just a continuation of the A/B services with a likely spark plug change, and in many euro markets a euro level check of the rear axle diff.

If you do the work yourself the U.K edition Haynes manual 3511 is a good purchase.