Sorry Dugald, but I have seen several threads about the chain problem on the 560. (Got worried if it was also the case with my SL500 2001).
So please do a search. I understand that it is recommended to change at around 150,000 miles

Here is one: http://www.peachparts.com/shopforum/showthread.php?t=213598&highlight=timing+chain

Anyway, a good preventive maintenance after you buy the car will save you lots of $$$, + you know "where you are".

Regards, Per.