Recently I've bought a used heatsink. It seemed good, except the base was dirty. I thought it was just a thermal paste.
But apparently it's not. Looks like melted metal. As if the CPU (Intel 370?) melted onto heatsink. Strange, but could it possible? If the CPU had burned out, maybe he temperature was high enough to melt it?
I don't know what should I do with this heatsink now. I tried cleaning it with various solutions and also tried to warm it up with a lighter. Didn't help.
If you, or previous owner, had an de-lidded CPU I might think that was it. The marks that you are seeing is just probably the outlines of the thermal paste burn-in for a CPU. I've had plenty on my aftermarket HSFs. If you don't feel any defects with finger then move one. There is no use worring about something you will never see.
this looks strange. if i were you, id buy a new heatsink, and return thisone. or if you dont have money, sand it with progressively smaller sandpaper, until you get to watersanding. then it might be good enough again, but thats really hard to achieve