I have just spoken to Morgan about the problem. One of its electrical boffins told me:
1. That this is a problem more prevalent in 2011-14 M3Ws. Since then, an improved sender has been fitted. He claimed that the older ones will show zero when there is about a third of a tank left; the newer ones when there are c.two gallons left.
2. That fitting a longer sender is unlikely to help by itself as the fuel gauge is calibrated to the factory-fitted device.
Firstly, many apologies for resurrecting this thread! I’m just wondering whether any folks with a newer M3W (2015 onwards) can confirm that their fuel gauge does indeed read ‘0’ at around 200 miles. If so, what is the part number of the fuel sender used? Or, maybe it's the same sender and the difference is that since 2014 they have been factory calibrated?