I bought a new 4120 in 2005 and it had been great. I am very thankful to have bought it when you could still get an American made , pre tier 4, JD power tech engine . JD has long had the best part support of any tractor manufacturer.I own a 4120 hat and I love it . Have grapple, bucket, forks. Use it all the time.I also have tiller, disk, spike tooth harrow, three pt spreader and MX 6 clipper from Deere. I did not want the yanmar, engine and wanted it built in USA. Mine has the Power Tech engine and the tractor was made in Augusta GA and wanted the three tier and not the four so it does not have the burn off feature which is what I wanted and got it the last year they built the three tier. Love it. Also my friend got the one that replaced it and lot of changes. The pedals are not heavy like on the 4120, mine are made out of same material like in the bigger tractors not flimsy like the ones they put on now.
I am more confident in continued availability of parts for the power-tech engines than I would be for the Yanmars.