The V-12 engine is bullet-proof and will last twice that mileage, easily, if it's been cared for.
However, the W140 car has it's own list that is long of things that wil eat your bank account. Things like AC evaporators, hydraulics, electrics, etc. The V-12 engine bay is crowded, and even simple tasks mean huge labour bills and expensive parts.
This car will probably eat thousands of dollars a year in routine maintenance and repairs. Keep in mind the original MSRP, and the buyer profile. MB never thought for one second about "economy" when bringing that car to market.
If you have the budget, a W140 S600 is a real treat!
1998 C230 "Black Betty"