Update - it's been almost 3 years since I bought the 300SDL. In that time, I've put almost 30k miles on it.
Around 6 months after I bought it, some crazy driver on the SoCal freeway crashed into my 300SDL, destroying the driver's fender, damaging the rim and causing some suspension damage. His Toyota pick-up was completely destroyed in this collision, but my 300SDL managed to drive off the highway, so I could wait on a tow truck!
The insurance company totaled the car and gave me a few thousand $ back. I took it to a good body shop where the car was inspected on their jig, and it showed no frame damage, I then paid close to $4k to rebuild it, as in my mind it was still a great car, and had proven its worth. They replaced all related suspension components, put a new hood, new left fender, clip, light, repaint, etc and the car looks just as good as I bought it. I have since put Ronal R9 rims on it and we continue to drive it on long road trips. Twice, I've loaded it up with camping gear, and even with 4 people we've easily driven up the CA coast to Big Sur, and up the winding Highway 1. I've never doubted the reliability of my 300SDL.
Last year I renewed the cooling system and used Zerex 3G, replaced trans filter/fluid and filled with Lucas oil, replaced serpentine belt, and also put in a new alternator. I also replaced the neutral safety switch, put in a new brake master cylinder, and repaired the rear window regulator when a small plastic guide broke. The car is quite easy to work on, so I do most of the maintenance myself. I use Lubro Moly full synthetic oil, which I replace around every 4k miles.
Overall, I am still very pleased with my 300SDL. I plan to drive it until it dies; maybe before that I'll buy another clean 300SDL to keep as a garage queen, so when this car dies I have a ready replacement. Definitely the best car I've ever owned!