buy or not ?

hello to all s-class drivers! play for a long time with the idea of getting me a s-class. but I have been a happy bmw driver for a long time. a 530i with many extras. but since I am a lot on the road and do not want to give up on much comfort I think about a s500 after w220! since the 7er of the design does not appeal to me as the s-class. so my questions would be there problem with used s-classes, what should be taken into account, there is a big difference to the 430 or 420 my is e in 430. how is that with high km performances? think also of a diesel only one hears that the are vulnerable that is true?