Having followed the various articles in the mags on stop cocks and what they are made of, I changed the engine (SC) as the handle had come off and guess what it is brass. Not marine brass. The others look fine but will be changed next year just incase.
If you are examining BWL metal fittings, the skin fittings are worth looking at too. One of the more vulnerable areas is the thread where the seacock fits on. Then the hose tail itself. the Seacocks are large heavy gauge metal and its the thinner threaded areas that can become weak. I have just been through all this on a Powerboat. Lots of information here: http://www.coxengineering.co.uk No connection, but these guys were great for the new parts: http://www.asapsupplies.com
Many thanks, I have looked through the various comments and will carry out a further check next yera I did clean off the skin fittings and looked for any change in colour.