An economist would say that when considering buying this machinery the farmer would also consider the cost and availability of repairs and that the competition in the machinery market (the primary market) would police the secondary market for repairs. In reality, this kind of policing is hard to come by because of the time and expense of figuring out which company has the cheapest lifecycle1 costs for the equipment (…
I'm pretty sure the farmers know very well the lifecycle costs of their heavy machinery, the problem isn't ill-informed consumers. The problem is the time as well as expense of repairs is controlled by the manufacturers. The razor example isn't analogous here, you can pretty much plan for when you need new blades. A farmer can't predict when the equipment will break down.
But the homework the farmer (or any purchaser - this same issue arises for medical imaging equipment, cars, busses, etc) should do is what will the service market looklike for his or her equipment after warranty. It's not easy to do this research - but the flip side is this: if the manufacturers have to sell unlocked service, they will charge more for the original sale. Economically speaking that may be better because the costs will be clearer.