EF600 fuel leak in fuel valve

[paul-r]

I have a EF600, fuel is leaking from the side of the fuel valve below
the fuel tank. There is a small hole in the side of the housing - fuel
is leaking from there when the valve is turned on.

I have dis-assembled the fuel valve, cleaned and re-assembled, it is
still leaking.

Is this a common problem ?
I suspect that the round rubber fuel valve inside the unit may be
leaking, is this the most likely cause of the fuel leak ?

thanks
paul