300 has EGR which it is better off without, 300 has rubber doughnut on prop which wears out... 200 has neither of these... 200 is less err complicated, older and cheaper?
some parts on the 200 are getting harder to find (like the exhaust front pipe I've just won on ebay for £25... yippee) but come to think of it, that is the only bit I've had trouble with and it's 'cos it's an auto!
although the same basic engine... the turbo is slightly different and there are 2 alternater/powersteering belts on the 200 and only 1 big one on the
300, some parts like the radiator are not a straight swap 'cos the plumbing is different etc...