I think luck plays an enormous part here. Most 211 owners on here swear by them and as has been said pre-2005 not really good a good period for any MB. It's a shame you have had a bad experience.
I am now nearly 11 years and 80k miles in my 2000 S210 320CDI and apart from a few majors (gearbox and head gasket both in last two years) it has been on the whole a hassle free car and I will probably replace it with another MB when the time comes. That is also influenced by a good relationship with a trusted MB independent (PCS in Horndean) who has looked after it.
I bought it 'eyes wide open' after a long search as a one owner 5 year old car in full knowledge of all of the 210 issues. It still goes like a train, although I've never achieved more than 37mpg in contrast to what I read on here. It has so far been very resistant to rust which is not to be expected for one of these. It does have a niggling recurring fault at the moment which I think is something electrical and connected (no pun intended) to rear lights.
At this stage anything we encounter with it prompts the 'repair it or scrap it' question. On the basis that anything close to it for performance, comfort, space and equipment is going to cost upwards of £20k for 3-5 year old car it's an easy choice, despite it failing most people's 'economical repair' test.
Don't desert the brand just yet - there are some great MBs out there, even if they do require a dedicated thorough search to find them.