That 01 S600 has an entirely different engine. Its the M137 that only survived for 2 years. They're known for out of round bores and lackluster performance at 362 hp (the same as my C55's naturally aspirated 5.4 V8).

My car has the M275 engine that has been enlarged to 6.0 liters and given a pair of turbos. In 2013 it was rated at 621 hp and 738 lb/ft from 2300 to 4000 rpm. Non-AMG versions are 5.5 liters and produce either 493/590 (2003 to 2006) or 510/612 (2006-2014). Mechanically, the engines are bulletproof. The coil packs are still expensive. In 2013 the SL600 got individual coil packs and that was carried over into the other platforms.

The biggest problem with a V12 Mercedes is not the engine itself (barring 2001-2002 cars) but rather the rest of the car around it. These engines didn't come in the simple cars like my C55. The cars have every bell, whistle, and party trick MB could throw at them. When it all works, it's beautiful. When things go south it can get expensive.

Stick with the newest V12 car possible. There were big improvements in 2007 and again in 2010. You'll note that mine is the 2013 and the last of that chassis style.