MASSEY 3090 INJECTOR PUMP LEAKING???

G'day Fellas -

I have a fuel leak from the IP on the above tractor - pictures to follow.
Just noticed the other day although I suspect what I always thought was an oil leak is in fact a fuel leak but is now bad enough to be a concern.

In the pictures that will follow there is a disc like structure on the LHS of the pump. This disc has a hole (manufactured) in the centre and it appears to drip fuel repeatedly while high idling. It looks like it contains some sort of diagpraghm judging by...

MASSEY 3090 INJECTOR PUMP LEAKING???

MASSEY 3090 INJECTOR PUMP LEAKING???