Well, the fuel mileage results are in :

1st tank since repair - 355km/39 litres (abt 9km/litre)
2nd tank - 395km/44km (abt 9km/litre)

My fuel mileage prior to the problem with the FD was 10 to 11km/litre so I will be working on the car to achieve that!

The old FD was taken apart but the particular nozzle on 1 of the 4 outlets (which appears blocked) is inaccessible from inside of the FD so looks like it cannot be repaired.

When I took the FD apart, the little o-rings inside were perfect, so were the o-rings for the EHA.

The plunger seal was not leaking, so I guess the problem was that one particular blocked vent which somehow screwed up the mixture and caused my car to run super-rich.

Anyway, I also learnt that my car has no CAT, and if it had one it would have been screwed up!

Cheers.