This is a tough comparison. Since 1983, a whole fleet of new regulations on smog control, recycling standards for components, and gas mileage rules have created a different environment for engines - hotter, more stressful, etc. This means more computer controls, and greater trade off between the competing tasks of performance, emissions, mileage, and reliability. Most modern engines hold up pretty well, but none that I have seen are without potential for failures - the sheer number of added controls and requirements makes for greater chance of failure. You are looking to compare a low revving, low power, basically unsmogged diesel to a high revving, high power to displacement ratio, heavily smogged, gasoline engine! The gas engine can't win on a non level playing field. And the diesel can't compete on the emissions playing field - get rid of the particulate problem, you trade for a NOx issue. Clean out the sulphur, you have a COx problem. No one has found a way around that yet, even with CDI, and most atmospheric chemists and health effects studies indicate the particulates are a worse health problem than gasoline emissions. (And I am sorry to hear that - I like diesels a lot!)
All that said, the m111 4 cylinder in the C230 (not compressed) seems to be a tough little workhorse, especially by 1997-98. Great mileage, and pretty respectable power for its size. The m103 I6 cylinder had valve guide issues, the later m104 apparently can loose head gaskets, but have reputations as strong engines. The 1990 plus m119 v8s put out enough heat that they could fry the engine harness from what I have read. (note the hood vents in the new MB E class!) The new v6 engines are supposed to be really great - Larry Bible did a review of a torn down m112 engine describing all the trick design features that sound like they are designed to last.
M112 Engine Review There are lots of other threads on each of these engines in the archives. A search will give you a lot of valuable info on each of them. Good luck with your search.