Water damage ... Errormessage there's not original accessory attached

Hi, i got an iPhone 3Gs which has fallen into water ... two days later it worked very well, but sometime there get up this errormessage that it is not original accessory attached ... after that the normal speaker doesn't work ... after the next errorpopup the speakerfunction get back ... cleaning the connectorport with a brush didn't helped really ...

what can i do to get this errormessage away?

is it only oxidation and I've to open and clean everything from it?

thnx a lot!

:)