Thanks for the responses - lots of things to think about there.
For what it's worth, I sail and I used to dive, hence my healthy respect for the sea! Thinking about it, with a few phone calls and a bit of blagging, I might be able to get in to a helicopter ditching simulator through work - worth a try and better than a day in the office. I've already done a sea survival course but no harm in being well prepared.
I have also experienced the 'auto rough' mentioned above - both in an aeroplane on the way back from Jersey and also at sea when the engine note in an old boat seemed to change the more the wind blew up!
I also get the point about not taking an aircraft straight out of maintenance on a 'difficult' flight. Best to give the 'F*** up fairy' chance to work her magic whilst options for a safe return exist.