Hello I have a 2003 ford explorer. While driving I tapped the brakes to come a stop but the brakes did not stop immediately. I had to press all the way down on the brake pedal for the truck to slowly stop. I pulled over and noticed the brake light on my dash board was on and a dark brown oil like liquid was leaking from my rear passenger tire.
You have a rusted steel line or the wheel cylinder blew out. Neither of those are especially expensive or difficult to repair. The exception would be if the rear brake was worn out and grinding metal-on-metal and you ignored it. Be aware though that as a result of pressing the brake pedal further than normal, that can damage it on any vehicle more than about a year or two old, so don't be surprised if after the repairs are completed at the rear, your mechanic has to tell you a new master cylinder is also needed. There's no way for him to know that right away but many shops will warn you ahead of time to prevent surprises later. Even if your master cylinder is okay, some damage may not show up for a few days. When and if it does, it results in a slowly sinking brake pedal when you hold steady pressure on it, and the red warning light will turn on again.