There are a bunch of things that need maintenance as mentioned elsewhere on this forum.
Lets see if my memory is still working......

Brake fluid every 2 years
radiator coolant every 3 years
spark plugs every 4 years or 100K
engine air filter every 4 years
cabin filter every so often, I do it once a year (dont' know official time for this)

Seems like the MAss Air Filter is a very easy change and very common wear item for all Benz's. Not cheap though...