It is a wet disc brake system which has 4 discs total. Think of it as a motorcycle clutch setup. It is immersed in the transmission fluid. While it can be worn out, it would take a long time for it do this. Tractor currently has 2,500+ hours on it, and I'd like to say I've probably "rode" the brakes well over 50 hours in it's lifetime. Brakes still work fine, and I've yet to adjust them because it holds just fine on inclines with load. Besides anytime I am on an incline, I drop the loader on edge to dig in a little bit if it does decide to move.
I still remember when I first got my BX back in 2002, I accidentally mowed the entire lawn (4 hours) with the brake engaged. Felt dumb.