any class 8 will give you better everything than a class 7,the only thing a class 7 may be better at is fuel savings,and that is if they dont use a tandem axle,put that 3rd axle on the ground and the class 7 fuel economy isnt much better than a class 8
as far as leaking oil,if you idle your truck,and dont idle at at least 1000 rpms,some engines 1200,you get oil slosh,it will seep out of turbo and run down side of engine making you feel the turbo is bad,another thing,ive owned all the different engines,never have i had a motor leak a gallon of oil on the ground,espedially when brand new,if i did,hello warantee,going to spend time in the shop at their expense