While I agree with what youre saying, can we stop calling the corroded pins/boards "dirty?" Maybe I am being a grammar Nazi here but I think it gives laypersons the idea that they're "cleaning" the contacts, as if they are covered in dust, dirt, grime, when in all my years I have never seen a cartridge that was literally dirty, other than a copy of Thunder and Lightning where it was covered in this nasty grime.
I'm not sure the exact composition of the contacts. I always thought it was either gold or brass? Whatever it is, when it is exposed to the air, it tarnishes. That's why carts eork better if theyve been sitting inside dust sleeves for 30 years, unplayed. Don't know the science behind it besides just knowing the basics about how copper turns blue (Statue of Liberty for example)