be sure to check model specific issues, especially published Technical Service Bulletins
a couple of other anecdotal and cumulative data references
https://www.carcomplaints.com/Mercedes-Benz/E320/
https://www.benzworld.org/threads/how-many-miles-on-your-w210.1210910/page-31
there is no printed service manual for this model from MB. only online, EPC, WIS stuff
so if you are inclined towards DIY, there can be a steeper learning curve than other cars.
some owners spend to get a cloned STAR diagnostic multiplexor for their own use vs paying
$100/hr to the dealer. but there is no easy step-by-step on its use so that is another learning
curve to track....and lots of reading through various online MB forums for tips on STAR-SDS use.