Because BNB doesn't commonly find nice AU58 examples that look good and well defined. They aren't easy to come by. I don't mean to sound insulting, but has BNB really seen/looked at alot of AU58 3 leggers? Honestly, some guys look for the 'right' example for years before they find the 'right' one. Some collectors have looked for a certain coin with that certain look for more years than you've been alive. There are more well struck AU58 3 leggers out there, without a print. Just have to have patience.
http://www.ecinet.org/pinewoodcollectibles/pvc_damage_is_caused_by_storing.htm Here is some handy info...
Why don't you just experiment with various methods using non valuable coins and see what works best for you ?
Don't know that I would say most, but there's sure a whole lot more of them than there used to be just a few years ago. And I agree :thumb:
I've had some good luck soaking pennies that were grimy in this stuff called Greased Lightning. It's for cleaning kitchens, but experimenting with soaking coins in shot glasses seems to have turned out well so far. It won't bring the date back on a Buffalo nickel or anything, but it does de-gunk a little better than Goo Gone so far.