I spoke with Quick Performance and their guy said the breather vent was probably bad. It's a new vent from DR Diff. The vent cap is floppy loose, not like the one on another 8.75 rear end I have. could that be the cause?
Yes, it could be. I had the exact same problem with an aftermarket vent. My theory is that the spring the holds to vent closed is weak in the aftermarket vents. I purchased an NOS vent on E Bay, Mopar part number 4032798, make sure it is NOS. Also, put your car on the ground, no jack stands, and remove the fill plug. Gear oil should be 1/2 to 1 inch below fill plug. Yes, thread sealant is a good idea to prevent threads leaking. Mine does not leak after I changed to NOS vent and made sure gear oil level was correct.
