I'm surprised that the 12.8L Mercedes is still available. Is it a current year model & is it the MBE 4000?
At any rate, I have the 12.8L Mercedes in a 2005 Columbia tractor and am completely satisfied with it's reliability and performance. At nearly 600,000 miles it is not using any oil and as strong and fuel efficient as always. Ive never used any fuel additive and have never replaced an injector, unit pump or turbo. Under warranty I've had 2 EGR coolers replaced as well as 1 head gasket. ( the Mercedes has 6 individual heads). Compared to other motors of the same vintage, the MBE 4000 is the most fuel efficient and trouble free of them all. I would buy it again.