You haven't said the depth or diameter or whether it's a through hole--if it's six inches across and a sixteenth of an inch deep the available options are different from if it's a sixteenth of an inch in diameter and six inches deep.
Have you determined the process that is resulting in the sticking (like is something melting and solidifying or is there a permanently tacky layer within the workpiece or is it all just naturally sticky--what works for one problem won't necessarily work for another).