Well here are some of the things I think about at your mileage, that is if you're not already doing and or should have been doing right along (you did say you'r following theservice manual:

Wheel bearings - all wheels.
Timing chain or belt and associated hardware, guides, etc - not sure about your car if it's belt or chain, I think all Mercs are chains.
Flush all flushable fluids.
Alternator / brushes, mine crapped out at 100,000.

I am sure there are a ton of other items. I would replace stuff just to replace though.

For example, front end suspension and stearing components will probably need attention soon but there are a lot of variables as to when they'll need to be replaced.

Joel