Maybe try sticking it in the freezer for about 30minutes, if that doesn't work, a soak in rubbing alcohol to dissolve some of what is gumming it up. If the
threads look to be cross threaded, :/ may not be any other choice to try forcing the lock ring loose, could possibly scratch and score the metal depending on what you got available. Once everything is loose and taken apart, clean all them threads and possibly polish and clean that nasty
mod if it looks grimey.