I love the W140 chasis.
I think the main weak points to check on would be:
1. Engine wiring harness: '93- middle '95's had bad harnesses. It may have been replaced, but if it hasn't and it fails, budget about $850 to replace it.
2. Head Gasket - the head gasket design on the early M104's was not good. It probably has been replaced at this mileage, but check for an oil leak at the right rear corner of the head (passenger side). If it leaks, you can let it leak oil until the leak gets so bad that it bothers you. Budget $1,200-$1,400 to replace the head gasket.
3. Evaporator - the early W140's have evaporators that leak. It's about 25 hours of labor to replace one, plus the cost of an evaporator. I'm willing to bet that the car does not have the original evaporator.
You should get a Master Vehicle Inquiry run at a dealer, and it will tell you what recall / warranty work was performed on the car at the dealer. Because this is one of the earlier models, I'm willing to bet a ton of things were performed under warranty.
None of these things would prevent me from getting the car. I'd just need to know what has and has not been done before buying the car.
I'd also insist the car had a full maintenance history, or I wouldn't buy it. On a used car, especially one with over 100,000 miles, maintenance is everything.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".