1927 China Memento Dollar - Grade?

Soaking a coin in acetone is pretty harmless. It dissolves paint, gum, oil kind of deposits but won't affect the coin's metallurgy.
On a few of coins of mine, transferring from retro plastic pocket to 2x2 I soaked each one for 15 min in acetone, then washed that off under running water, and allowed to dry naturally.

They did not seem any different. I knew however they had been 'degreasified' ready for their new home though I don't think it was essential - just a fussy thing to do.

The darker patches on your coin are probably from handling over the years, and the fingerprints have affected the surface, but I don't think there is anything sensible you can do about that.

I can only assume that, after looking at these pictures, that my example of this coin must be a fake. I will mark it's holder accordingly. Can't remember where I got mine from now, so I will just put my head in the sand and rekon that it perhaps did not cost me too much when I obtained it.