Injection pump leaking

[LondonDave]

I have a Kubota M7030SDT with the V4000 engine. From what I've figured out it has a CAV rotary injection pump. The pump is leaking from the side that faces into the engine. It's leaking from a small needle and seat type valve where the rod that the fuel shut off rides along. There is 3 washers on this valve that seem to activate it when the fuel shut off is pull out or pushed in. I'm sure there is a name for it. I just don't know what it's called. I have a mechanic friend (not a diesel mechanic but can fix just about anything) working on it for me. He got the valve out without taking the pump off but he said it looks as though it's not serviceable.

Is anyone familiar with this to tell me what the fix is? Is it a pump rebuild?

Thanks

Dave