I had the problem with my Pioneer couplers, that would disconnect themselves, and had to recouple them to get everything working again. My new tractor has the flat faced couplers, and I should have changed my old tractor over to them a long time ago. They are so simple to use, and I haven't heard of any failures as of yet. I did hear about leaking problems with the 4 gang disconnect on the loader on the BX23S, however that was a while ago, so I can only assume that Kubota has corrected that issue.
If I were to need couplers, I would either source them at a Parker dealer, or from a Kubota dealer. There is no savings, when you find that the quality of the product fails shortly after purchase. Many times, parts come from China, and the price is good, but the quality isn't. Ever wonder what happens to parts that don't meet quality control standards? Many times, they are sold at a discount to people wanting to save some money.