i got under my x and noticed that it looked like there was supposed to be a bung or some kind of hose attached to the rear axle. after reading on here i believe that it is the "breather hose". my question is what does this do. i took it to the dealership to get an oil and diff oil change, they didnt say anything to me about the broken part. is this somthing that needs imideate attention or what, i have no idea what it is to be honest so im in need of some major help here.

thanks to everyone who can help