My 2 ton disappears it's brake fluid during extended periods of storage. I never find it either. I think it goes trough the hydrovac into the engine and gets burned up.
Last week the master cylinder was dry again. I used my one man bleeder valve which has a ball bearing and a spring. I can pump about 5 times before having to refill the tiny master cylinder resevoir. But 5 pumps was enough to bring clear fluid even to the further wheel. So, I refilled the master four times and the brakes are great again.
