To be honest i do not know enough about the 600's to give you a reliable breakdown of costs. The general consensus is that they are massively more expensive to service due to coil pack issues and plugs being hard to get to, but as i say i really dont know enough to go into detail.
I believe that all 600's also come with ABC (active body control) as standard which from what i have read (purely from what i have read, i have no personal experience with ABC failures) can be massively troublesome and expensive to the extreme if/when it goes wrong. I can back this up by the fact that most places will not work on ABC systems (including merc specialists), and that i have never seen any ABC parts for sale anywhere other than Mercedes directly making them very expensive.
Your budget wont get an F/I car, so it would be the N/A 5.8L V12, which although fantastic, i dont think its worth the extra potential hassle over the (excellent, and bombproof 5.0 V8 with airmatic suspension rather than ABC).
I'm not sure what you mean about facelift power increase on the 5.0? The same 306PS engine was used throughout as far as i am aware. The facelift brings improvements to all of the electronic systems, the fibre bus, the nav, etc etc. You wont get a facelift in budget though.
All i can really say about buying a 500;
- Bodywork - corrosion - normal checks.
- Underbody - corrosion - normal checks inc exhaust system, cats are v expensive, check them - one each side.
- Check that it starts on the first crank, every time, that it warms and idles at ~400rpm
- No malfunctions appear on the dash computer
- The suspension raises quickly and uniformly when you press to raise it up, if possible try loading something heavy in the back, check that the ride height does not differ from when unloaded, the airmatics will compensate.
- Airmatic pump should only run for approx 20 seconds upon cold start, no longer, and shouldnt need to kick in again more than once every 30+mins - if more frequent possible leak.
- Xenons - check all modes, the ballasts are made of cheese.
- Comand - instant satellite lock, check cd changer comms, check phone comms, check dash comms (dash screen and steering wheel controls).
- Doors, boot - offer them into position and they will self close, little air pump can fail which controls this, so check it.
Other than that...nothing specific as such. Just make sure everything works really. But take more care than usual as there are a LOT of systems. Press every button, seat heating/cooling, all seat modes, memories, all keys, the lot. Dont assume anything as these cars are getting old now
