Cat 740 transfer case oil in front diff

Hey Guys, hoping someone could point me in the right direction. Working on a Caterpillar 740 ADT S/N AXM00773 with approximately 13k hours on it. Oil is leaking from the breather for the front axle housing. I'm guessing the Oil is coming from the transfer case and getting in the front axle when the diff lock is activated. Does this make sense? I will not have access to SIS or a service Manual until sometime tomorrow and was just trying to get a head start.
I've never worked on this...

Cat 740 transfer case oil in front diff

Cat 740 transfer case oil in front diff