I have two salemen that always stop and wanting me to buy amsoil and schaffer oil. Never heard of schaffer but amsoil yes. Then there is quaker state, pensoil, and list goes on. I use cenex oil, grease, gear lube etc and have good luck. Never had a problem. I am running all synthica oil in trucks but I still run regular oil in mowers cuz I change oil b/t 75-125 hours and that it seems like every two weeks things are being changed and with the frequency of changing why go with syn. oil. And then each tries to sell something different - 5-40 vs 5-30 and they even told me they have a 0-40?? Unless you guys can sell me on the "right" oil - I am sticking with what I have used.