Does the sender earth through the screws from its cover plate or is there a separate earth connection? I have got a 2013 wiring diagram, albeit only A4 size so you need a magnifying glass. The sender appears from the parts book (V.5.2 - Fuel System Right - P.26) to be integral with the pump - part ref #6 unless it is what they describe as the "fuel tank dip pipe" - part reference #10 and this page shows the wiring (P.69 top right corner).
Wilson
No the sender on the M3W is separate from the pump although there was one integral to the pump for use on other applications such as Land Rover.
The earth connection to sender is a tag in wiring loom which connects to the senders body via one of its mount bolts as you suggest.
Picture here of 280mm sender with 750 ohm shunt resistor fitted.
This gave the best results for me although there were still random fluctuations. Generally I only got a consistent 0% gauge indication after at least 200 miles with plenty of reserve.
