I have a 1999 2,4 JTD, now done 320 000 km. I love the car to bits. More torque than my previous 164 3,0, and as quiet. My impresions is that the 166 is a much better car than the 156. Roadwise it is a car that is easy to as ask for a danse, and it danses extremely light footed for such a big car
So far the engine has been pretty good, and stil do not have exessive oil consumption. (aprox 0,5l / 15000km)
things to look out for on the diesel:
stay away from cars that have been tuned with "power boxes" (a proper chip from reputable tuners is ok) (power boxes mess up the egr system and reck havock with the dual mass flywheel)
The dual mass flywheel need changing at some time, it shows up by noticable engine vibrations around the 2000rpm mark (i mistakenly thought this was an engine ecu issue.) Mine started to do this around the 200 000 km mark, but I did not change the flywheel untill 300' km
The Turbo is a variable vane thing, this variability stops varying at some point (mine did at aprox 300' km, but again power boxes can cause this to hapend much earlier) This shows up by the engine warning light comming on when full power is applied, and engine cutting out if full power is aplied for longer period. (new turbo is the case if fixed by a workshop, but it is posible to dismantle the turbo and clean it up if you do the work yourself)
As with all modern engines the mass air flow metre often gives upp to the ghost.
I have heard rumors that the early 175 hp engines sometimes has valve trouble, but i have no idea if this is correct or not.