I have a 2005 4120 power reverser with 1000 hours on it now, and it has been a very good tractor. My only complaint is that the original Bosh starter failed from corrosion, when it was about 5 years old. A factory replacement starter was big bucks back then, so I opted for an aftermarket "Powerstrike" starter.
That has been working well for the last 11 years.
The only other parts or maintenance that tractor has received has been engine oil and filter every 100 hours, coolant flush and change in 2018, new front tires in 20l6, and a new battery in 2015. It has never leaked a drop of any fluid. I have also never changed the hydraulic or fuel filter. I do use deisel fuel conditioner all the time.
I have had as many as 4 other tractors, most of the time I have had the 4120, and it is mostly just me operating. That is why the hours are low on it. I have been thinning the herd a bit lately, and now I am down to just one other (my first tractor, a 1951 Ford 8n).
Wrenching and maintenance are easier on the 4120 JD than on the old Ford, but the old Ford is a lot easier to change 3 point implements on. I suppose that is because it was the model that first brought us the 3 point hitch, plus it is a lot lighter and easier to muscle around.
Oil filter changes are particularly difficult on the old Ford. The only wrenching the JD has needed in 16 years has been the starter swap, which was a piece of cake 10 minute job. The worse job I had to do on old Ford, was changing the distributer last winter. It took me most of a day to get the drive gear on the right tooth.
