I was under the impression that the wiring harnesses were bad only from 1993-1995, and only on all M104 engines - on the C, E, and S classes - on the 2.8 and 3.2 liter engines.
The wiring harnesses on the 1990-1992 3.0 liter M104 300CE's were fine.
While there might be wiring harness issues with some 400E's, it is not systemic to the model, and not due to bad wiring insulation, but maybe chafing of the wires.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".