The 1987 300D (W124) is an awesome car, far more advanced than the older W123 chassis. The OM603 engine is very robust, and our friends in Finland have been able to triple power output (450+) using custom turbos & intercoolers. But the 603 engine is not quite as "bulletproof" as the older iron-head OM617, which was pretty hard to kill. I've owned several of both and I have no interest in going back to the older chassis OR engine.
Here's a buyer's guide for the 1987 300D/TD that you might want to read:
http://www.w124performance.com/docs/mb/articles/124.1x3_buying_tips.txt
