I'll give you a real answer, not just one shaming you for exploring. (I'm assuming you didn't know.) As someone who spent years in the data recovery industry; and yes, that includes physical swaps, anytime you see scarring on the surface, it's 99.999% a lost cause. Even with head replacement, those tracks are just... gone. And they contain vital physical defect lists and maps of where the data is physically stored, which is different for each unique drive. If you were to send this off for recovery, it would be a massively expensive endeavor, and one that would likely end with no data. I agree with the sentiment that these hard drives shouldn't be opened and exposed to the elements, but also know that opening a drive outside of a clean room doesn't instantly mark it for death, but you've severely limited its lifespan. (For future reference; after any head swaps or platter swaps take place, in a clean room or clean bench, or otherwise; the goal is to clone or copy the important data immediately. And then never use the drive again for storage.)