Today I had my radiator changed as the old one had a very small leak. It never leaked enough to notice a drop in coolant so I've never been worried about it running low. The old rad was completely rotten so it was a good thing I swapped it now. All topped up bled through and looking good on that front now I'm not sure if I didn't notice this before but there seems to be sludge in the overflow. Header tank is clean, no bubbles in overflow and oil cap doesn't have cottage cheese so I'm ruling out head gasket. My question basically is What is this stuff?? Maybe it's some old remnants of a kseal attempt?
Would do you guys think?[emoji54]