Help! Fuel level issue

[dougal]

When I bought my 2001 X5 3.0D 2 years ago it had an issue where when the fuel level goes below 1/4 level it starts acting as though there is a lack of fuel like difficulty starting etc..

Now its worse, its doing it with between 1/4 and 1/2 level on the gauge.

I was told in forums it could be a fuel filter or the pump between the two parts of the tank.

I went into the hidden menu in the cluster gauge, I think 6.2 and it said "TNKANZ: 74:8L PHASE2" and I read online that it could be a problem with the sender unit sensor/s.

I took it to BMW and they said that BOTH sender unit's need to be replaced and that one costs around 115 euro and the other is around 490 euros because it has a pump.

I would rather avoid such an expense. Should I replace one or both and any tips where I can get them cheaper like third party etc ? Also could they be fixed ?