Albeit true that MB's have charm, character and a devout following, any old or used car will need repairs sooner or later. I have slowly come to this realization that my 84 300D will never be factory new and always require fastidious attention to operating normalcy lest some unforseeable/ unpredictable mechanical cough/hiccup occur.
I have easily spent 3x what I paid for the car on a full suspension rebuild/upgrade, body work due to NE rust, new tires, steering adjustments, drivetrain repairs and normal wear and tear parts, such as seals, gaskets, the everpresent broken VDO malady and I havent even begun to look into an A/C rebuild/update (at least the compressor isn't siezed). 3 out of 4 windows work and the "power sunroof" sounds more like a power shi*-roof due to the stripped SR gear and rusty tracks.

That being said, I truly hope the 617 engine holds true to it's venerable reputation. My mechanic has said it is one of the nicest sounding 617's he's heard in a long time, but Im not sure if thats a line he uses with all his customers who have just forked over their weekly paycheck for a repair to make them feel better.
I will NEVER part with this car. It has become like a little brother to me, has its vaccume quirks and electrical gremlins- but I love passing newer cars on the highway at 80 up a hill with no problems and people just look at me like im nuts.
So, no matter what vechcle you decide on, unless it's under warantee, you just might want to reserve at least 1/4 of your budget for immediate maintanance and repair. I wish I had, but that still would not have made a difference in the cost or getting my girl up-to-snuff.
Happy hunting, I'd suggest finding a low mileage W123 and taking her for a Italian tune up then pointing ot to the owner the leaky valve cover gasket, worn belts and any other deficiency you can find in order to drop the price!! I ran away with mine for 1k! calculated milage is slightly over 100K miles. Not bad for a Boston car.
Ben