My 97 1ton dually has a braking problem i think the master cylinder is leaking. but there is no booster behind it It has a valve with 3 lines running to the power steering pump in it's place. My ? is would the master cylinder bleed though that to make my firewall wet inside and out.

Are you loosing fluid in the power steering or brake fluid?

The brake pedal pushes the rod that activates the brakes like any master cylinder. The booster assists the brake pedal. The hydroboost replaces the vacuum boost seen on some gas powered models but works the same way.

When the seal goes you could have fluid inside and out.

I am loosing brake fluid

Sounds like the master cylinder to me.