Amsoil 15W40 in both.Had 600-700 hrs on M4700.Only have 100+ on M6800.I think I put it in at 75hrs.In my truck and VW I use the 5W30.Been using it in my trucks/cars since 1985.Never had any problems,leaks.It is good oil costs a little more but in the long run it is cheaper.
When I put it in mt M4700 it had 50 hrs.on it.I don't know of any engine that want run on synthetic.Before I bought that m4700 I had a ford 801 40hp diesel.I used cheveron delco 400 in it.Sold it to a friend of mine and he switched it over to amsoil 15w40 and its still going.You can imagine how many hrs are on it.It was a 1960+ model.You want have any problems with it. Everything I own I use amsoil(your choice but I don't think theres anything out there better).Pig Boy(brother-in-law) switched his ford tractor over,60+hp
Installed 15-40 Amsoil in John Deere at 50 hrs and complete hydraulic system at 50 hrs. VW turbo deisel 1000 miles 5-30. Ford Powerstroke 1500 miles 10-40. all three deisels do not use any oil. Gary Amsoil dealer # 386195
Gary I have a Powerstroke (97')and are you running Amsoil 10-40 in there? If so, that is not the correct oil for the Powerstroke. You will mess up injectors. I hope you Amsoil dealers are give the guys some product cheaper? /w3tcompact/icons/wink.gif