John,
Any safety device like a GFCI(RCD), can only be depended on if it is tested regularly.
They have a test button on the case of the unit for a reason, unless the end user is not being made aware of the need to test these devices (which is another issue in itself) monthly, of course the mechanism is going to freeze up, it isn't like a contactor that moves at least once or twice a day, every day.
