OK, I've got a '98 model.
The X plate will be the larger 2.6 engine as opposed to my 2.4, but its the same engine, pretty much.
Firstly, the enemy of the 210 is rust (really!), so check all wheel arches, tops of doors, wings, bonnet and bootlid, particularly around the boot release button. If the car has a full history, chances are the dealer will pay for any remedial work.
Oh - also check the front cross member as this can also rust.
Engineering wise they're pretty bullet proof. All my has had done is a new MAS at 98K (a common weakness), other than that its had a new headlight unit (PCB failed) and a new aircon condensor radiator (didn't use it enough). Aisde from those items, the car has been regularly serviced.
Tyre choice seems fairly critical on the E-Class for the best ride. I've had Continental and Dunlop the last couple of times. Avoid Pirelli P6000, as the ride on them is dreadful, and the tyre tread design is way past its sell by date. Dunlops were very quiet and wore reasonably well. My current Contis are okay though.
The auto box is allegedly filled for life, but a change of tranny oil will restore the silky smooth changes. Don't be concerned if the car holds gear changes longer when cold - its the car trying to warm the cats up as quickly as possible. A gearbox oil change will set you back around £150 - £200 from a dealer. A good indie can reduce this to £120 easily. The ride is firm without being overly harsh. I test drove an Elegance at the same time and thought it a little too wallowy for my liking.
My car is near to 159,000 miles. I have every confidence it will hit 200K without a hiccup.
Choose carefully - there are loads out there. Don't be afraid to test a 320 (petrol) - the mpg is almost the same as a 240, but the engine has a healthy dose more grunt.
Good luck!
Greg
