Been away, but it looks like you got some very good advise. I seen in the photos your boat came with very good servos! Back when Kyosho sold these boats with the servos and radios included they came with the Futaba S38001 sail servo and the S 3004 rudder servo. Sadely Futaba decided to discontine the S3801 the do still offer parts should you ever need them.
It appears at some point there has been some water inside the hull, and rusted some of the screws that hold the servos in place. It is always a good idea to keep your hardware as clean as possible and free of corrosion. Make your your connectors are not rusted inside - can prevent a proper connection and flow of electricity.
Another thought beyond the balloons, would be to put a piece of sponge in the hull to absorb any small amounts of water that may make it inside the hull. Be sure to remove it when you have finished sailing for the day and remove any water still in the hull. Also when not in use, leave the boats hatch cover off to let any moisture trapped inside to dry out.
Kyosho sells parts from their web site so should you require any replacement parts they are one possible source. I image there are a few local hobby shops in the UK that sell parts for these boats as well.
Here is a link to the Kyosho parts web page here in the US. They may have one over there as well. I have ordered from them and had no problems.
Enjoy your new boat.
''Windchaser"