Done, Thanks to Royse,Carb Shack Gary & Lisa For advice and support. I posted the decal on the oil filter canister cause it says change when dark on dipstick. The manual is in hrs of service. An non-detergent oil takes a long time to turn dark. Detergent was not available to the public till late 40s or so I have read.I have owned this N for 35+ "working years" plowing, disc,sprtooth,blade,Tiller, yes a Tiller (they are not suppose to work on Ns) and bush hog. It never had anything but non-detergent straight weight.Still runs 30 lbs hot,no smoke and ya can still hear the lifters. It was used and never abused. She is retired. Thanks For Looking