Did you properly aerate the box and pump before driving?
I remember after I installed my 1st gen Borgbox the fluid was foaming quite a bit after first startup.
I let it sit for a few minutes for the foaming to reside, fill it up a bit then start it up again and turning the wheel lock-to-lock.
Had to do this 2 or 3 times before the foaming stopped and oil was at it's proper level.