Barrs stop leak ??

[Waldoe]

I bought a 70 gmc about a month ago, as far as the motor and tranny goes, runs great, no water in the oil, no tranny fluid in the water. Shortly after I got it I noticed the overflow tank was dark looking, so when i looked in it,it was very dirty. The truck had been driven about 3000 miles in 5 years supposedly. Took the tank off, cleaned it out real good, put it back on. couple weeks later I noticed a small radiator leak after it runs for a while. Truck runs great, did not get hot. I also had new fan belts and wanted to replace the hoses anyway. When I went to take out the radiator the water that came out looked dark brown. At the top of the radiator,where the fill cap is, water is green like antifreeze. The thermostat was also stuck open. I could see where the radiator had been repaired several times before. I decided to have the radiator rodded out and "rebuilt". Decided to change out the water pump also, flushed out the block backwards, and the heater core. It was full of dark brown water. At first I thought it was oil. Put it all back together, filled with straight water, The overflow tank is brown again, looks like wet clay in the bottom of tank. water is brown again in radiator. I pulled out some of the "clay" and put it in a container. I am still filling and emptying the radiator. Hopefully is is some type of stop leak that someone has put in there. I have put stop leak in my radiator about 40 years ago, but would never do it again after seeing this.I can see how it would work if this is what it is, but I would rather fix the problem. In the pics, notice how the water is brown, then after it sits, the water turns green like antifreeze, and the "clay" like stuff settles to the bottom, looks like mud, when dried it looks like dirt. Look at the blob of stuff on the side of the container. After I saw it dried, I put it in a clear glass. Opinions??