There are two gaskets on the N oil filter. One under the clamping bolt head and the other is a large rubber one under the cap itself. The small bolt gasket is a hard fibre type and can be bought at any CNH Dealer. Ask for part number 01A-6749. Don't try a steel washer as it won't work. Ten or twelve years ago you would get one in a new oil filter element kit, but they no longer include it. Often times they wear out after many oil changes and will leak. The large Rubber Gasket is usually included in a new filter kit. Some brands won't have it. Get a FRAM CP3 or one from your CNH Dealer to be sure. There is a cheaper FRAM model, CP but it has no little steel handle to help removing when needed. As Soundguy said, be sure all surfaces are clean and free of old gasket material before installing the new one. Take a dab of clean oil on your finger and smear all over the new large rubber gasket before installing.