John Deere is. There are policies for when a part can go out of production. I can't talk about them, but it amounts to if it is replaced often it remains in production. (My local dealer has the oil filter for my 1939 tractor in stock). Electronics are tricky - chips from 20 years ago are not made anymore, so if that electronic system breaks you are done. We try to predict how many replacement parts will be needed and make a large final order but sometimes we are wrong.

The fact that we make replacement parts longer than our competitors is one of our big selling points.

#deereemployee, but not speaking for my company of course.