While I agree the value is negatively influenced by the additional marking of unknown origin, the primary value of the pistol is based on the amount of original finish and whether all parts are correct and/or original. More and much larger, detailed photos are necessary to comment on whether or not finish and parts looks right. However, it looks pretty glossy to me for a pistol in that serial range. If refinished, the C could be the refinisher's mark or an owner's mark. Who knows without better and more complete photos?