It was the stock fluid from the factory. I did add Redline water wetter but that was it. I recall early on that when I checked the rad fluid the upper tank was all orange and this orange stuff was floating on the top of the fluid. I mentioned this years ago when I bought the WRX. Others seemed to experience the same coolant issues to include the paint on the inside of the tank top where the rad cap is peeling off and heading into the coolant passages. I had taken my tank top off and removed what was left of the paint.
The sludge is really weird, I wonder if all the low lying coolant passages and areas are packed with this stuff?
But whan I changed the rad fluid it was clear and not orange discolored.