My dad found a 98 freighliner 120 with an 18 foot grain bed on it. it has a M11 cummins and 9 speed transmission. air ride rears and brand new roll tarp. my questions are. how are the M11's? are they good and reliable.   The truck has 9xx,xxx miles on it. would this motor have been rebuilt by now? What should we expect when looking into this. Dads current truck is a 79 ford l9000 with an I6 detroit and ten speed with spring suspinision with about 450xxx on the odometer. Whether that is original or not im not sure.  What should we look for if we get a chance to look at it?
Thanks! 
Austin