Here's what I would do.
Buy the part from Messicks or another Kubota dealer, regardless of cost.
Pay someone local (preferably a competing Kubota dealer) to install it, fit the backhoe and test everything out
Sue their ***** in small claims court for every cent it cost
But BEFORE you do that, I'd recommend reading this:
Writing A Demand Letter That Gets Results
A 'demand letter' is a wonderful tool that I have employed to get companies to do what they should know to do anyway. It is a clear way to spell out what the agreement is, what is expected, what you've done, what they've NOT done, and what WILL happen starting now. Include sales contracts, cancelled checks (copies), receipts, detailed phone records and other records of contacts and visits to the dealership. **This is basically all the evidence you would / will show to the judge in small claims court** Send it registered mail and wait for a quick phone call.
I used this tool on a contractor who was quite reluctant to finish the job and I had a phone call within a few hours and a tractor trailer full of equipment at my property the next day. 48 hours after the ink dried on the letter, PROBLEM SOLVED.
Don't give up the control you have over your own situation. Their responsibility is to make things right. If they choose not to, YOU make it right and make THEM pay for it. Very simple concept.
I wish you luck, good Sir.