It depends on how it has been maintained. Are there service records? Has the PO done everything to maintain the car? Was there preventive work done or did they wait until something broke before addressing the problem?

I bought my 420SEL, which is basically like the 560, a little over 3 years ago. I have been doing little odds and ends to it since - usually something every couple of months or so. I have been doing these things either myself or with the help of a friend who is a MB tech.

If you can do some things yourself it won't be as expensive to maintain if you have to have someone do everything for you (don't mean to make a brainless comment to insult your intelligence - after all, you are considering a Mercedes ).

If the car has had the timing chain, tensioner, and guide rails done recently then you are in good shape. Another thing to worry about on this model is the hydraulic suspension in the rear. Does the car "squat" in the rear? If it does, walk away because it means work to the rear $u$pen$ion. Valve stem seals and valve guides are another "weakness" of this motor. The bottom end of these engines are usually "bulletproof" and don't require anything until several hundred thousand miles.