Brake issue

I'm hoping someone can give me some insight to the issue I am having.

I was leaving for work one morning and while I was leaving the brake has zero pressure and only stopped at the last few centimeters of the brake pedal, I looked under the truck and pulled the wheels off and couldn't find any leaks, now the brake fluid has gone down since but im lost on where to look and what my next steps are.
The rear wheel cylinder were rebuilt last year at Toyota and ive looked at the master cylinder on the inside of the truck and found no moisture at all.


Edit: i ended up taking off the master cylinder and found brake fluid in the brake booster, and also discovered the seals were bad on the master cylinder.

 

Inspect all of the brake lines from the master cylinder down to each wheel cylinder, caliper and if it is a manual transmission check the clutch master and slave cylinder along with their tubing. If you don't locate a leak and are loosing brake fluid there isn't many places for it to go. Such as the Vacuum Brake booster sucking it up and burning it in the engine. Inspect the inside of the vacuum hose from the vacuum booster to the engine for brake fluid.

 

If you haven’t been or have never adjusted the brake shoe self adjusters, a likely location is the wheel cylinders. Possibly, they’re over extended and popped out leaking fluid all over the shoes & drums. You might see the drums & back wheels covered in brake fluid. Since the drum is a cup shape, sometimes it will contain the leak & you won’t see it until you pull the drums off.

 

He updated his original post.
It was master cylinder leaking. (into the booster)