Nice job on the repair, however I'd re-approach Kubota and ask them nicely to pay for the repair. While I can't examine it myself, and the pics only show a little, and only you know if there was some form of abuse? (You avatar does show a large stump?)
My thoughts only, the second picture says it all, abuse doesn't appear to come into it.(**). The machine is designed to do a job, the design of hydraulic cylinders, pivot points, leverage, is all governed/controlled. No matter what you do hydraulic wise if something breaks, there is a reason. The reason appears to be metal fatigue due to an incorrectly designed dipper. It appears the metal has sheared while in normal use doing the job it was designed to do. Is the damage/wear to the machine elsewhere showing abuse/twisting/overloading of the boom etc? The bucket and dipper from the pictures appears to have very little wear/use on it.
** However, if they can show that there was inadequate/no lubrication to the pin and the dipper was seized to the pin and when the bucket was rotated it sheared the dipper or they can show that the hydraulic relief settings have been set out of specification then that is a different story. The thing about a frozen pin, the pin needs to be frozen in the bushes of the dipper, the bushes themselves need to be frozen in the dipper, and the pin needs to be frozen in the bucket bushes, bucket bushes frozen in the bucket, because the only thing that stops the pin from spinning is the bolt going thru the end which would shear of in an instant.
EDIT: A bit late now, but looking again at the pics, the possibility of undercutting of the parent metal of the boom from the factory welds around the pin bushings may have attributed to it as well, being the initial failure, as it appears that it was cracked some time ago.
