Never saw a milk spot on Perth Mint coins and I hope to never see that on any in my possession. As for phillies and maples, milk spots are common. Removing them through scrubbing (with eraser or cleaning liquid and cloth) gets rid of them once and for all, but leaves little scratches on the surface (visible if you look real close). Not that it matters for those coins. Anyone tried cloudy ammonia? Heard from few sources that it gives great results, but never tried it myself.
