Hi
Did you ever get this sorted out ?? as I have today done mine and you do NOT damage the water seal if done correctly as implied by an authourised supplier, in fact I would say this one (unlike the older Braun models) is designed to come apart easily. and when put back together will infact be watertight again.
Why would you want to spend another £70 on a new handset from an authorised braun agent when to replace the battery is simple, and when it's only 2 years old I think its a waste of Money.
I will gladly post full photos and instructions if required
Pat-UK
October 2009