Vauxhall Omega Fuel Guage - Not reading "Full" when tank brimmed ?

Hi there.

I have a V plate Vauxhall Omega 2.5 V6. I noticed this gremlin last
time, but just thought I was too frugal filling it up !, but I brimmed
the car FULL with fuel today and the fuel guage again fails to read
Full. It seems to settle at 60ltrs with the needle at about the 1
o'clock mark, with full in the past registering with the guage
pointing fully vertical ?

I have just had the connector off underneith and cleaned all
connectors and WD40'ed the plug - No change.

Any thoughts ?

Andy.
.