I just bought this John Deere 8960 tractor from the dealer. It has 544 hours.
It works fine, but I have noticed a gas leak around the prime button on the fuel / water separator
The priming pump is a separate and replaceable part, but it probably cannot be repaired.
Your dealer should offer to replace it with a new unit (according to their agreement).
This part is just a personal opinion – my experience with John Deere XX05 and XX03 series tractors (admittedly limited) has been primarily in two areas.
Electric, and fuel. The overall fuel system is poorly designed to begin with. The tank outlet is mounted low in relation to the engine.
There is no supply pump, so the entire system relies on the transfer pump in the injector pump to draw fuel from the tank.
The fuel filter base is mounted higher than the injection pump, it is also empty while running, so any leak allows air into the system.
There are solutions to all of this, but they will come at your expense, as neither Deere nor the dealer will agree to supply any of this.