I have a 2015 Charger RT 138k miles. At 97k miles had the water pump replaced, has ran good since then no issues. Noticed a few weeks back this stain on my motor that looks like it somehow came from the hose connected to the water pump. Maybe once every 2 weeks I might have a little steam come from under the hood shortly after starting the car and then would go away. I finally brought the car to a shop that I feel I can trust. They have been doing a little testing on it and the coolant had a sludgy material in it. This is the main reason I brought it in because it was brown and I didn’t want to risk driving it more and having a major issue. I was told they think stop leak was added to the system which is why it went to a brown color and told me when they opened the valve on the radiator nothing came out. Obviously that concerned me even though I didn’t have issues with overheating and kept watching the temp, I ranged between 190-210 which from what I was aware is normal. Based off the pictures I’ll add. What do you guys think I’ll expect to hear back about when I get a call? Is this fixable like in terms of flushing out a clog somewhere or will I end up with having to get a lot of new parts like a radiator water pump etc. the mechanic shop I brought it to, my friends dad works there for the owner and he’s super nice. I believe I’ll actually get treated right on my car for the first time so I do want to believe everything they say since I’m getting picture updates from my friends dad. 

Hemi 5.7L cooling system question