My father delivered his '94 C280 (280.000km) to the dealer, to fix an oil leak. After the leak was fixed, the car wouldn't start. The cause was found quite easily: all insulation of the cables in the wiring harness ("kabelboom" in Dutch, in case somebody's looking for this keyword) was turned into powder! It was all cracked, exposing the copper wires.
Dealer never saw it before. We think he was honest.
Mercedes Customer Service Benelux thinks this is "normal" for a "car this old": the "rubber" of the door seals would also "get hard" after this many years. I asked them why the dealership never saw the problem before. No answer... Then the dealer told us that -to his surprise- the wiring harness (a 1000EUR part) was in stock at Mercedes Belgium, and according to him this would mean that the problem wasn't exceptional...
Then I searched Internet only to find out that about every (94-95) C280 owner in world gets confronted with this 'normal' problem...
For details, this is a good starting place:
PS: my father ordered a new Toyota right away - the number of problems he had with the C280 is endless, this was just the drop that made the cup run over...