I have bought some figures from The Plastic Soldier Company and they have sink holes in the plastic. With what do you close the sink holes on hard plastic figures? Green stuff, liquid green stuff, putty ?????
I ask because of accessibility so you can fix it, if in a thought spot i would suggest something like Vallejo liquid putty since it dries a bit slower and is workable, so you are able of doing some "sculpting" if needed, this is my choice I reckon you will receive more input from other member's so share with us the results.
For Plastic Soldier Co figures and vehicles, guns etc, (which are in polystyrene,) fairly deep sink holes or major inaccuracies ( eg Universal Carrier - visible joint line on vehicles sides) I find Squadron White Putty to be the best. For small holes or tiny gaps left with multi part figures Vallejo body putty is very good and has a smooth finish.