Dear all
I have a new 2018 M3W since one year and have drive around 8500 km. I live in North of France and use if for meandering on the coast border and for driving in Belgium
The bevel box was yealing a lot at 60 /80 km/h and I bought the bevel box vent from morgan custom net. Oil contend switched from 400 ml to around 830 ml and the sound decreased a lot ( Have tested it for 500 km, incredible, my hear were quiet) . No noise up to 80 /100 km /h, and lower sound.
I have have modified to system to be able to fill it directly from my rear car boot. Filling is tricky and I heated the W 140 : pb of air that has to go out . Just some patience needed, It takes 30-60 min. Slow flow of heated oil ( W140 has a high viscosity @ 15°C ).
Make me think that bevel box noise is more linked to the level of filling than of the quality of oil . Anyway the ride is now quieter :-) 
Have some pictures but not able to download - you can download it from hyplinks below
https://www.dropbox.com/s/o7gqsx8nfr7t5tr/BB6.JPG?dl=0https://www.dropbox.com/s/98xfpnp08aionzk/BB2.jpg?dl=0https://www.dropbox.com/s/idws3hvhjc26i08/IMG_20191022_102457.jpg?dl=0https://www.dropbox.com/s/1mfzrmh0j2qdb5m/IMG_20190825_123547.jpg?dl=0Hope it will help you to go through this issue
Note : Have also set up the oil cooler and the ventilator temporisation for summer - all fits and run perfectly . I m very happy with the reliabiliy of the M3W
With warm regards from France
Franck
