Winch plates bent on my mast winches

[ttex]

Corrosion.

Water is collecting at the bottom and hanging due to surface tension. Once corrosion starts at the bottom it will spread upwards.

[Pollux]

Thank you all for your ideas and knowledge, I appreciate it. Personally, I don't think it is made by someone trying to steal them. It has been coming gradually, first on the starboard winch and then on the port one. I know it's not done by overload, since we do not use them. For the sails we have, everything is controlled from the cockpit.

My assumption is (after reading yor replys) that it's due to corrosion between the bronze winch base and the aluminium mast. I will remove them, try to bend them back, and then properly reattach them with insulation between the metals.
Thanks again.