My last car before the current fleet was a 1986 euro 300D. They're good cars, and plenty fast - just like the older NA 300D's were also quite decent - the turbo doesn't add /that/ much without tuning. That said, I found the car slower than an OM617 turbo - I got a 0-60mph time of 18 seconds, which my thousand-pound-heavier 1980 300SD will beat, not to mention the 300CD. I wrecked it though sadly, thanks to bad alignment and letting the rear tires go bald without noticing.

You may note from my signature that I no longer have any car that new. The '86 was the fourth Mercedes I owned, and the newest. In my opinion, the W123/W115/W114 and W116/W108 chassis' are the best Mercedes ever made and have a lot more style than the newer models (W124/W126 and up). And while the OM60x is a little more powerful, the OM615/616/617 is more reliable and easier to work on. So if I were looking for an older Mercedes diesel to play with and learn on, I'd go for a W123 - they're currently still quite inexpensive and soon the easy pickings will be gone just like they are for the W114/115. If I were looking for something larger and classy, I'd try to find a good deal on a W116 300SD (they still exist, though not as commonplace as W123 deals).

That said, the W124 is a good chassis too. It's the last E-class chassis built by hand, and while lacking the chrome and details of the older models, does have a pretty modern look to it. Since Mercedes produced this chassis through 1995, nobody will guess you're driving a 1986. It's got some neat newer features like power seats. And well, the newer parts are, the less soon they will need replaced, as a general rule. The price seems quite decent as well. Mine cost me $1500 but took thousands of dollars of repairs in the first several months of ownership. :/