If it isn't leaking due to overfilling with oil, or you failed to install the rubber flat gasket under the lid, then it's probably the 01A-6749 lid bolt seal has failed. Shown in diagram as p/n 18675, the bolt seal is a fiber type material and works great. Twenty-five years ago when you bought a new FRAM C-3P or equivalent oil filter, you also got in the kit the large rubber flat gasket that goes under the lid and the 01A-6749 bolt lid gasket. Nowadays when you buy a new oil filter, even from CNH, you don't get that 01A-6749 bolt seal, and some don't even give you the large rubber flat gasket. I know the FRAM C-3 filter doesn't have the little handle on the top of filter to assist easier removal when you change the filter. The good news is the part is still made and sold at CNH -SEE PIX. Now some fellas may have had better luck than I using steel, copper, nylon, or plastic washers for the seal, but I never did -they always still leaked. About 16 years ago I bought a handful at my local CNH dealer and stocked up. Also good news is that first seal I bought in 2003 is still on my 8N oil filter housing so they are reliable. Fellas have a natural tendency when an oil leak pops up to simply try and tighten the fastener. Overtightening will cause warpage and you don't want that. The large flat rubber gasket under the lid must be applied with the lid free of all old gasket material and debris. As Bruce said, apply the new gasket with clean, fresh oil all around before setting into groove on lid. When assembling lid, start the bolt by hand and apply mild pressure down all the while turning the lid to seat properly. Once lid bolt is snug, then tighten and don't over tighten. Next, fill crankcase with clean, fresh oil BUT only put about 3 quarts in. Capacity on an N is 5 quarts PLUS 1 quart for filter absorption, BUT never refresh with 6 quarts total. You will want to only put an amount to get dipstick up to line level as marked. 4 or 5 quarts max at first. Run tractor hot, let cool down for a day, check dipstick when cold. IF level is still is a tad shy, add small amount to bring up.
FORD OIL FILTER:
FORD N-SERIES TRACTOR OIL FILTERS & CANISTER LID WASHER:
FORD N-SERIES TRACTOR OIL FILTER HOUSING LID 01A-6749 WASHER:
*NOTE: Newer MPC lists the part as 18675 as shown in the first picture but the OEM part is 01A-6749.