"I like the snob appeal of having a relatively new MB, but the classic lines and beauty of a well kept 300D can't be beat. On the other hand, I'm in business and sometimes having a decent Mercedes shows that at least I had the common sense to make some money in my career."
Not sure if a C class would give off that impression. An E class yes, but a C class says to me "I'm trying to act important/ I have a lot of money". Not that there's anything wrong with the car, it just seems like a car for people that want to try and show off. Kind of like the Cadillac Catera. I'd sell it, personally I would Never own a newer Mercedes. Like everyone else said previously, they have to much electrical junk that always goes wrong. Buy a nice 300D. However, since your in business (as am I) you probably travel around to different towns/cities. So maybe the best thing to do is Purchase something newer. These cars are great, don't get me wrong, and i have taken mine many times to down town Chicago, Wisconsin, the Suburbs. But that's not without consistently keeping it up (which is pretty easy). Would i take it to California? absolutely, it would be an adventure meaning that i would be pre-pared for a break-down or anything else that might happen. That's why i purchased a new car (that and i needed some speed

). I trust the ol' girl, but i needed something with less "adventure". A vehicle with a warranty.
If I were you, personally, i would sell the clunker C class, and buy something newer, and a more reliable brand (speaking of the new MB's). If you like luxury, purchase a Lexus or Acura. Even Hyundia has a nice new luxury car that out performs Mercedes and BMW.
Just my opinion
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1983 Euro 240D 277K
2016 Mazda 6
Coming Soon, 2013 Mercedes E350 Bluetec
Formers:
2012- Mazda 3
2007 Outlander- complete pile
1995 E300 Diesel 208K
2007 VW Passat 2.0T

63K SOLD
2003 Jaguar X-type 3.0 Sport Sold 04/11 w/88K
2009 Lexus RX350 9061 miles. Sold 04/09
2008 Mitsubishi Lancer GTS:Totaled Sept.,09 @ 24,000
2003 Infiniti I35 58K Sold
1984 300 turbo diesel 222K