If this is the same DR that makes the DR trimmers/mowers and such, I've always had good luck with their customer service people. Nice, friendly, and hablais Englais. They know exactly what parts you need and they understand any common problems something may have. Call their 800 number. They take a card and ship fast. I think you can find parts diagrams and numbers on their website.
They can tell you whether it is backordered or not. Maybe the dealer has his own backorder. He may be right about 1 out of 2 not working but then they make their money selling new splitters and not $5 worth of parts. In their defense, they probably get complaints when they sell repair parts that don't work so they don't promote it. Besides they have to do what you should do, call DR and order it and pay shipping then tack on a little extra that probably doesn't pay for their time. Some customers find a new dealer when they run into ones that don't service what they sell.
Of course we all all shooting in the dark here as you didn't say what part was leaking and where. Pump, valve, cylinder, or lines/fittings are all possible options.