Filled my car up this morning with diesel from empty and the gauge took 40 minutes during my commute to get to 5/8th of the way full.

Checked it again about 1 1/2 hour later and its show nearly full (about right).

Any ideas?

Changed the fuel filter yesterday, but cant see any relevance of that.

I had a similar problem (not a VAG car though) and it turned out to be a sticky level sender unit in the tank.

Think it was around £30 for a new unit at the time.

I can't see it being anything but a sticky sender/float unit myself.

Are these serviceable or are they only replaceable? Could the potentiometer be cleaned?

When I took it out to have a look, it appeared that the potentiometer had worn very thin at the top end and was very clean, so I guess the resistance was wrong that day.

Got a part no of 8L0 919 673E from ETKA