[BonzoHansen]

unless you know you over filled your rear I'd doubt that is it, although overfilled rear may blow out the seals. I'd expect it to blow out of the vent tube too if that was the case. if the vent is clogged it might push out past the seals.

you have to open the rear to remove the axles. Inspect the axles for wear. Also check the outer axle bearing. I just had to replace those on my truck because play in the bearing caused the leak.

also, oil contaminated brake shoes are beat, so replace those too when you fix it.

Paul is right, also check your wheel cylinders.