General rule of thumb is, if the non shift motor came with seals on the drive and prop shafts, gear oil is the preferred way to go. Gear oil is neccesary on the Evinrude Sportsman/Sportwin motors equipped with seals and which have a ball bearing on the driveshaft directly below the water pump which needs oil to lubicate it. Grease of any kind will not be able to make its way up to this bearing. I’m not sure if the HD motors are equipped with this bearing or not.
JD Corn Head grease liquifies when worked so it will find its way into bearings and bushings just like oil will but a heavier grease can not. Gearcases without seals will allow oil to drip out and water to come in while the JD grease will not drip out as it solidifies slightly while sitting. Badly worn bushings on the shafts will aggavate this problem. Any water making its way in will be emulsified with the grease while still allowing the grease to lubricate the parts between servicing.The Corn Head grease isn’t recommended for any FNR shifting gearcase because of the way they are designed. They need oil to do the job.
If the gearcase has a vent plug on the side and quite high up, then it definately takes oil. This diagrm of a TD gearcase shows seals on both shafts so I’m assuming it requires gear oil, same as my TN’s do. 