You can mark the turnbuckles with a piece of tape wrapped around the screw part where it touches the body on top.. then loosen slowly (maybe two turns loose then go to the other side and do two turns there, then two more turns on the original, etc) and equally..Use a halyard on each side (main on one side and jib on the other) attached to the toe rail close to the existing shrouds(tension lightly) to stabilize the mast while the shrouds are off the chainplates. Pull the cotter pins and clevis pins once the shrouds are loose and remove the shrouds.. From the inside of the boat, you should be able to unbolt the chainplates and take them out for inspection.. When you go back up, be liberal with the sealant! .. Good Luck.