fuel guage probs

When I fill the car up, the fuel guage reads just below full. I have fueld up a number of times and have yet to hit the full mark. I never had this prob on my 02 MC - like in any normal car I was always able to go a 1/16 on an inch beyond full, but this is a prob on my 04 MCS. I have tried a number of things, pumping slowly, fast etc.

When I go into the diag mode in the odo readout, the reading on the left tank is always 5 litres less than the right tank.

So I had it into Mini this week, they replaced both sending units, seals, floats etc. I figured this was the issue. It was not. I still cannot register a full tank of gas.

Anyone know what is wrong? My dealer like me seems to be baffled. My next guess is that something is wrong with the insturment cluster, or the computer as the mechanical pieces have been replaced.