I love mine! 265k miles, and I have the original head and head gasket, turbo, and IP. My cooling system works perfectly and has been totaly trouble free.(because I replaced every last cooling system part 3 years ago, nothing lasts forever!
) I don't really have any oil leaks, doesn't burn any oil, always starts regardless of temp.
On top of that its pretty smooth, has decent power, and returns 21mpg-23mpg around town. Considering that a 560SEL in similer use would return about 12mpg, its a very good car for its day.
The 603 is a great engine, I have had mine for almost five years now, I'm never going to get rid of it. I have put a lot of work in my car, but most of that was into the car itself. The engine has been damn near trouble free. Actualy other than a few accesory problems when I first got the car, I don't beleive I have ever had an engine problem. Its been the most trouble free part of the whole car!