I have a TC-24D, but I would assume they spec the same oil. I typically buy the 10W30 Ambra, but I did buy some 10w30 from Napa when I first got it. I was more expensive than the New Holland oil. I've since found Rural King carries Shell Rotella 10w30 diesel oil. I've bought a jug of it, but haven't used it yet as I'm still depleting my inventory of Ambra.
BTW, according to my manual on the 24, you can use 15W40 above 32 (I think) degrees. For anything colder and general use you can use the 10W30. I just use 10W30 year round so that I don't have to worry about changing it when it gets cold if it isn't time. It gets used year round (though less in the winter) so I don't worry about changing it in the fall. I change it based on hour meter.