The M111 DOHC four is proving to be really tough and reliable, and the Kompressor version is beefed up even further to handle the additional ponies.
One potential long haul weak point may be the Eaton M62 superchager. (62 refers to displacement of the unit)
Similar units have been used by Ford and GM for some time. They are deadly reliable during their service life, but have a short expected life in terms of MB engine components. Most seem to give up the ghost sometime around 200,000-250,000 kilometers.
Not a problem for your Ford that's ready for the "yard" anyway, but an MB is going strong.
The main concern is cost when it's time to replace it. The price may be coming down as the Eaton units are used on many MB models, but last time someone I know checked it was about $4000 plus R&R. Of course, the supe seems to slowly give it's notice, so you could just sell the car when it starts to go...