My great-grandfather owned an Allis-Chalmers dealership in the 1950s. He bought his 1959 D14 brand new and it has been on the farm ever since.
It has been used almost every summer since about 1959. It easily has 3,000+ hours on it, but I cannot verify the exact hours. It still has the original engine and runs like a top. It typically burns 1 quart of oil every 10 hours or so but that is not bad considering the work it has been put through. Everything on this tractor is original and still works.
This tractor gets used for brush mowing currently but has been used for swathing and baling hay. It is a little underpowered for some heavy grass/alfalfa hay cutting but that is not surprising for only having 30 horsepower.