I've seen it 4 times on the same tractor! Same owner too. MX5100. This tells me that someone's doing something with their tractor that they shouldn't be doing.Remove the bolts on the left lift arm to remove it, remove the snap ring on the right lift arm to remove it.
Use a piece of wood or brass to drive it left to right.
And WOW, I've seen very few of those broken over the years!