Problem free, that would probably go VF-35 in my book. It has great color and an even wear pattern, nice strong wheats, just a tad away from XF-40. BUT, it is not problem free.
What grade? I don't think it's a question of "how would you grade this coin?". I think the question is, why buy a coin w/all that damage?.
To explain what has been said a little better you must realize that most type of corrosions, toning, staining, etc are the metal of the coin combining with something else. Usually Oxygen, not PVC. Regardless of what has caused it, the removal of the problem item, stuff, would mean the removal of some of the coins metal. In many instances this could leave pot marks, streaks, dimples, etc. If the so called corrosion is only surface contamination, possibly a little distilled water would help but I doubt it. The next thing is to stop any further problems, just make sure no air can get to the coin. Without Oxygen or other gasses making contact with that coin, nothing further will happen. The best thing to really do is spend your money on a better grade coin.
I would say 35-40. I don't like to net grade. I guess it's up to you if you purchase the coin but I would not count on making it look better.
I decided not to purchase it awhile ago, just buying problem free coins really, unless the deal is too good to pass up. If anyone else would like it, I'm not going to buy it. (MAN, this thread is pretty old. ) Phoenix