In addition to the other tips above, You might check the thermostat elbow on the cooling system to make sure it is aluminum rather than plastic - I don't know what year they switched to Aluminum, but it is a recommended retrofit. Also, My tech tells me that the most important thing with these cars is to do all the maintenance on time, every time, with the factory recommended parts. In other words, brake line flushes every spring (good to have an anual brake inspection anyway), cooling system flushes every other year with approved coolant (apparently there are lubricants in the "approved" lubricants that keep the water pump happy).
I have had my car about a year, and the best advise I can give is to find a good tech you trust, follow his/her advise, and stay on top of the maintenance - neglected maintenance will bite HARD. Also, to keep it looking great, Follow Lee's Detailing FAQ's under the do-it-yourself heading at the left side of the page. I just thought my car was clean when I got it - after Dr. Lee's treatment, the car looked better than any 300E I have ever seen! Good luck, and the people on this forum are GREAT about answering any question that can be dreamed up about these cars.
87 300E, 65k miles