Just throwing it out there, but that particular V12 isn't known for being one of MB's better engines. They had a lot of reliability/durability problems and MB dumped it for a new engine after a very short time. Was this engine tested as solid/good before all the mods done to it? A lot of them had issues with rounded cylinder walls and such causing compression loss/other issues.

They should have used an M120 motor, those are beasts!

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)