advice on buying s320 cdi 2001my

i have always wanted an s class and am looking at a 85000 miler wth service history (allegedly). I have read lots about expensive failures and unreliablity, i will probably do less than 20000 miles in the next three years, so should i take the plunge or is discretion the better part of valour?
The car has a new MOT with no advisories.

Previous form: 1993 W124 220 petrol auto for 8 years

Thanks for your time