I checked my rear differential oil today and it.

I checked the hose that suppose to release the pressure out of the differential and it was clear but then I checked the fitting that screws into the rear end that the hose goes over and it was clogged, I then cleared the fitting using a piece of wire and cleaned it and reinstalled it. I am thinking that this was my problem because it was building pressure and could not release or vent that pressure and it was blowing oil out of the rubber plug that goes into the fill/check hole in the diff cover. I am now waiting overnight to check the oil after it has time to cool down and check if it is still foamy if it is I am thinking that moisture may have contaminated the oil and I then will take the diff cover off and drain the old fluid and refill with new fluid. Also the oil that I am using is Motomaster Synthetic 75W90.

I also have another question about the side axle seal on the front passenger side of the truck. I had a mechanic replace the seal about a month ago because it was leaking gear oil on the rim and was very noticable and now it is leaking again. I do not know how long it has been leaking or if they damaged the seal while installing it or is there another problem making the seal to leak. The vent hose is not clogged like the rear diff so it should not have blown the seal because of excessive pressure, but I always keep the diff oil topped up because the pinion seal is leaking oil bad. I am going to bring the truck to a different mechanic next week and see if I have better luck this time. Thanks for the information.