I don't want to frighten you but I bought mine S500 one year ago with the exact same mileage of yours and since them I already done the following works:
1) Replace the switch at the gearbox, made the ASR light comes on and the engine loses power, very hard to find out;
2) Replace motor mounts, with 126kmiles they are gone for sure, makes o lot of difference;
3) Replace the electronic adjust throttle sensor;
4) Replace the complete cablage that connects the modules box to the engine, quite expensive but these cablage really turns bad with age, check yours;
5) Replace main fan hydraulic clutch;
6) Replace thermostat, very important with these mileage is probably going to fail very soon, and can cause serial damage to the engine
7) Replace front suspension soft mounts, completely gone at 126kmiles;
8) Replace nitro cells at back suspension;
9) Replace complete transmission shaft, it had a permanent vibrations at around 60 mph;
10) Replace fuel pumps and fuel filter;
11) Several others little things, such as filters of all kinds, power window system, electrical antenna, key ignition...
I might had not too much luck with this one, but almost all these cars that haven't a rigours maintenance jobs, and believe me the dealer papers does not mean much, mine also have the complete history at the official Mercedes dealer.