installed new shocks today, noticed i have gear oil coming out of the seal between the rear diff and the drive shaft, so i went to top off the differential, make sure im not low on fluid.. taking off the filler plug released a lot of pressure, i really cant figure out why, i took the breather hose off and its clear, hooking up compressed air to it, there is some pressure build up, theres a white cap at the top of the breather, it seems to be blocking the airflow some, but not enough to build up the kind of pressure ive got there, not sure how i would test if its clogged at the differential, kind of thinking it is, i stuck a coat hanger in there and hit something pretty solid feeling.. anyone know whats supposed to be in there?