Don't have a OBD 2 if not get one as low as $12 it's not fancy but even without a check engine light there are systems you need to check some times you will find codes without a check engine light. smog coming up? before i had a OBD 2 my HC was to high never knew my EGR was clogged until i bought a OBD 2, or don't go to the dealer to find out what is wrong with your car plug in the OBD look up the codes online like i did and that is it, fix it erase the code if it doesn't come back it is fixed. The main point is you want to know what is going on inside the trans & engine which can be done in two ways #1
is take out your engine & trans and open it up or #2
have a diagnostic tool to read if there is a issue or not. Finally your transmission fluid should be changed every year doesn't matter what the dealer says and oil on a Mercedes should be changed every 1-2 months or the minute the color changes, And a sure way to ruin your engine is not checking your coolant tank and hoses. My coolant hose blew i drove over 4 miles without coolant the engine temp was reading still good so i kept driving was playing music so i did not here nothing until the car sputtered then died smoke everywhere i thought the gasket was blown the sparks was dead, but nothing was damaged, but i was lucky! Now the coolant in just as important in my book. Lift open your hood every day look under your car every week the goal is to know your car from the inside out. if your Mercedes is happy you will be also. And for gods sake polish every 6 months & wash under the car too that's it cheers.