Don't let any of this scare you. I've driven 123 cars many totally trouble free miles. When I bought this one for my daughter it turned out to be less than it appeared and additionally the person lied to me about oil consumption, which is one of the most important indicators about these cars.
If you have a car that has been well cared for, and you continue to give it good care, it will serve you well for many miles/years to come.
I do believe that, generally speaking, the four cylinder cars are more trouble free than the 300's. The four cylinders are much more simple to work on as well. Give me a four cylinder diesel 240D for absolute simplicity and long term reliability.
Enjoy your diesel,
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in