Welcome aboard!!!!
For more information, search "400E" and read other opinions.
Generally, the 400E is a GREAT, really great, car. It's about 75% of what the fabulous E500 is, which is a beautifully balanced sport sedan, and many people believe the W124 series cars are the last of the cost be damned, built to the highest standard mid size Mercedes, as dictated by the engineers, and not the bean counters, (as today newer Mercedes models are).
Their successor, the 1996 W210 series, had lots more electronics in them, and those parts did tend to give trouble, though not to take away the fact the W210 is very roomy, comfortable and smooth, though they tended to rust, in the spring perch and other areas.
But the 400E is a real tiger, it's very quick, and handles, corners and brakes VERY impressively, and will last for hundreds of thousands of miles if it's taken care of. The build quality is superb, and these cars are engineered to travel at their top speed all day long. These aren't just political promises either. Ask it to go----floor it at 80 mph------and it'll GO!!!
As to this particular example you are considering: You have done your due diligence, and had the car looked over carefully.
The miles, over 180k, might seem high, but you have said that they were mostly highway ones, which are better than a lower mileage car with mostly city and stop and go driving or short trips.
There is a verified service service history, which apparently shows the car has had good care, and the body is in good condition, I am assuming it is rust free and not a refugee from a freeway pileup that was rebuilt.
The problem typical problem areas, such as the wiring harness, air conditioner, and head gasket leaks, have been addressed or ar not a problem.
Therefore, there is nothing really wrong with the car. These cars are really, really, bulletproof, needing only the ocassional fluid and oil changes, and normal things like brake pads, batteries, shocks, tires and such from time to time.
The power steering gear box may need replacing, or the O rings on the PS pump, but at 180k, that's normal wear and tear, like replacing motor mounts if needed.
The small leaks mentioned can be monitored and addressed later, just keep an eye out. I'd re-read the service records carefully, to see for example, that
the timing chain, tensioner and guide rails were all replaced, as all should have been.
The mechanic correctly pointed out that this is a mechanical device, and as such, things will wear out eventually, so you need to be prepared for this.
But it sounds like the car has been given an overall clean bill of health.
A couple of more things, first, black is a very desirable color for these cars, although a nuisance to keep clean, and also the 400E was a relative rarity in 1992 compared to the ubiquitous 300E, of which there were so many.
With the diesel engine in them, they were the German taxicab, so they were built to take terrific abuse and still run hundreds of thousands of miles, and they are a VERY very good car, sturdy, and durable.
At $4,200, I would leap at the car. It's a very fair price for what you are getting, so long as it is rust and wreck free, and is as you have described it.
Just for fun you could try and hammer him a little bit, ask if he'd take $4000 cash in hand, but I would pay the full asking price of $4200 if he wouldn't.
If you are only going to travel 6,000-7,000 miles a year, it's not out of the question that even with 180,000 miles on it now, you could still expect to get 15-20 more years out of the car.
Don't forget too, if it ever runs out of gas, gets a flat tire, or a dead battery, any Mercedes owner can simply call 1-800-FORMERCEDES and they will send a truck out from the dealer (or a contracted tow truck in rural areas) and get you going, for FREE! It's a wonderful benefit for ANY Benz owner.
I would buy this car right away if I were you
For comfort, safety and even longer life I'd suggest you look into a set of quality fitted 2 piece sheepskin covers for the front seats (
www.ramsheadusa.com), a pair of front Macneill "Weathertech" black rubber floormats, and a set of european headlights (beautiful, 60% better light output and better beam pattern) and perhaps an upgraded stereo system if you want it.)