Are your chainplates mounted outboard or through the deck? If they are through the side deck there should be a rectangular plate which is notched for the chainplate with screws to attach it to the deck. Usually you would only need to remove that plate and rebed it. If the leak has existed for awhile you should look for "bleeding" below. If there is evidence of much rust, you would be well advised to remove the chainplate for a thorough inspection. If the chainplates are outboard you need to remove, inspect and reinstall them.