You need to reroute the breather hose to the pinion position. If you do not the differential will pump the
oil out of the differential and into the catch can while you are driving. You have to ask yourself, where is the
oil supposed to be while you are driving?! Obviously if the
oil is in the catch can it isn’t lubricating the differential like it is supposed to be doing. The other thing David mentions is that it doesn’t take much oil loss to damage the differential, while you are driving the differential can pump a pint or more of oil out from where it needs to be and into the catch can where it does ABSOLUTELY NOTHING! The catch can will only drain back once you have come to a complete stop, even then you have the oil that was pumped out of the catch can that is GONE until you refill the differential yourself. If your car is moving the differential oil will NOT return to the differential, the vent hose is not a two way street.
Yes, the drain at the bottom of the catch can can help to return oil to the differential but the capacity is far less than what will be pumped into it.
I find it puzzling why we are visiting this issue, for years manufacturers (Lamborghini, AC, Aston, Jeep, etc, etc, etc) have been using this differential with nothing but a simple vent affixed to the differential cover without issue, or leaks. Why was necessary to reinvent the wheel?!
I’ve attached a photo of what an original 289 Cobra differential cover breather looks like for reference, other manufacturers are not that different, it has a small floating cap to vent the differential to atmosphere and there are no leaks or fluid being pumped out because there is a small deflector welded to the inside of the differential cover to keep the fluid from being pumped out......