BCA,

I'll second everything Ashman and Dakota said. Especially about the head gasket and transmission. I found a 1988 300ce last Dec. that had 41,000 miles. It was a Fla. car and winter used most of its life. Had an MB dealer inspect it and they found a number of problems..some big (weeping head gasket at rear of head (replaced))and some small (pin hole in rear muffler).. The seller and I worked all this out but it was money very well spent.

If the mileage is only 51k, things like the paint in the wheel wells should still be in VGC. Mine were shining like new. How clean and dry is the pan under the engine. Is the exhaust original and what is it's condition. I'd say the system should still be original. Mine is!

I believe I have read threads here about wiring harness problems with some of the early 90's 124's..some other members might know more about this.
Not sure where you (or the car) are located, but the 51k reading is not really suspicious..probably accurate..some people don't drive their car(s) a lot, especially in areas where second or vacation homes are common.

Repeating those before me, get the VIN and do a carfax. find out where it's been before it got to where it is now..how many owners, etc. If it's been retitled a number of times, be careful.

Finally, thoroughly test drive the car under as many different conditions as possible. If you are not used to driving a W124 chassis, find someone who knows the feel, sounds and soul of this car.

If it all checks out and you get it, you are gonna love driving it just like we all do. Yours sounds like everyone else's ...drop dead gorgeous!!

Good Luck!
Jim