Welcome to the GKN problems club.
I had the same problem traveling to Moroco 16 months ago.
But my feel is that I have solved the problem for ever, i hope.
Make the tranfer vent hole biger.
Replace the big bearing in the GKN with another orginal bearing. Only the original NTN orange color will run ok, don't try SKF or other brand.
And install another seal and a o ring in the GKN, like you can see in these photo.
One travel from Madrid to Tunisia, and 20.000 km after, my GKN is working ok still, only with a small mix of oils between tranfer and OD.