Mine had a wet cover on it but it does not stop a buck load from a roof leak getting into the till, if the only answer is get a wet cover don't answer this question.
Can I dismantle the EX-A213 and get inside to check it out and see if anything can be repaired or replaced and if how, what needs to be removed to get in.

Paul, February 2011

If you mean the rubber keyboard cover, this is really a 'sticky finger proof' cover. It is not designed for full water proofing. If you want to stop things like leaks from affecting it, you should use a bar hood (perspex box custom made to surround the register - often used in wet bar situations).
Yes, you should unplug the register, open it and dry it out as soon as possible. Take the screws out of the bottom of the keyboard and dry the membrane inside the keyboard. Then give it a try.

Registerman, February 2011