I would spend a few bucks with a qualified smith to have the screws loosened (dismantle the gun?) so that any future endeavor for cleaning/ect. will not result in buggered original screws.
Be VERY careful about using ANY sort of polish or cleaner that is liquid.
The moisture in such products can combine with dirt & sloughed off corrosion turning those into an abrasive slurry which will instantly degrade any original finish or patina when rubbed or otherwise agitated to "make it work".
There are ways to remove corrosion and fouling without damaging the finish, but great care must be practiced. DON'T do it until you have spoken with an expert or you will affect the value of the gun by simply attempting to clean it.
Be VERY careful about using ANY sort of polish or cleaner that is liquid.
The moisture in such products can combine with dirt & sloughed off corrosion turning those into an abrasive slurry which will instantly degrade any original finish or patina when rubbed or otherwise agitated to "make it work".
There are ways to remove corrosion and fouling without damaging the finish, but great care must be practiced. DON'T do it until you have spoken with an expert or you will affect the value of the gun by simply attempting to clean it.