I really have to jump in here and agree with John (blackmercedes). I have owned Japanese cars for 17 years before switching to MBs (Hondas, Acura, Toyota.) All but the Toyota ate me alive in parts and labor after 80-100 k miles. These cars had been treated very well with Mobile 1, and with premium and early service.
By 120k miles, the 1988 Acura was costing me $4800/year average, (not counting tires!) and the glove box was filled with plastic parts that had fallen off various interior locations. There were many design deficiencies - 128 major TSBs on the Acura Legend compared to the 12 on the 1 year older MB (look up the NHTSA TSBs)
The 1984 Toyota has 250k miles on it, but the plastic and upholstery (despite being garaged at night and car covered during the day) are brittle and splitting, and the windows, hatch, and doors rattle, leak air, the body creaks, and the AC whistles because all the foam on the gates is gone, etc. It still looks clean and runs adequately, but is too noisy to bother upgrading the stereo, and would cost a fortune to restore.
The 87 MB doesn't have these problems. The body is tight, there are no noises. Looking at the repair records, the Japanese cars have cost me more per mile than the 300E (The Toyota is close to a tie. Parts on the Acura are 50-100% more than the MB, Toyota parts are 10-25% more than the MB, but the Toy has 3 times the miles, so I can't really compare!!!). There is no wind noise, and the underhood area is not the plumbers nightmare that the Acura presented.
A lot of people talk about oil leaks from their w123 diesels or from w124 300Es. I drive my 300E pretty hard, (as verified by the tire shop doing my tire rotations, and my tech during trans fluid and flex disk changes
) but at 85 k miles compression is perfect, it doesn't use a drop of oil between the 3k change intervals, and there are no spots under the car's parking slot in the garage. My brothers w123 300 diesel leaks zero oil at 180k, and the engine always looks clean. Go Figure!
Finally, my Japanese car mechanic of 15 years has repeatedly warned me for the last 5 years that I should not consider a Japanese car that is newer than 1990 with anywhere close to 100k miles - he says they aren't built to last, and he won't personally buy a new one, just lease for 3-4 years and walk away.
All this said, every car wears out, some faster than others depending on climate, driving style, maintenance frequency, skill of the mechanics, quality of oil and gas used, etc. I PROBABLY wouldn't buy a new MB with the intention of keeping it 15 or 20 years, but I DEFINITELY will not buy a Japanese or American car for long term ownership. If I were leasing a current model year car for the duration of the warranty only, it would be either MB or Lexus, depending on which one I liked best at the time.