Q: Truck idled, ran rough, fluid streaming from motor

A very bad knocking noise has developed in my dad’s truck recently. It has that sound as if something is loose. A couple of days ago when I was driving his truck and I got to his house, the truck idled, was running rough, and then the engine almost shut down. There was a stream of fluid pouring from the motor and so I opened the hood and saw that the master brake cylinder lid was loose and the brake fluid was spilling everywhere. Now, the truck has a muted knocking noise when I start it. My dad thinks he changed the oil and put synthetic oil instead of regular 10w-30. So I'm thinking that he did not change the oil and kept the same oil that was in it and just added the synthetic oil. I don't know if this happened or not. He’s a bit forgetful these days. I don't know if that is what would make the knocking noise, or not. Perhaps it is the brake fluid that has gotten inside the cylinder. The oil pressure lights read a bit high and my dad also told me that the truck has stalled coming up their road. Now he has no transportation and I want to fix this for him; he needs my help. We are hoping that it is a simple fix so he won't have to scrap this truck. In your experience, what will fix my dad’s truck?