Cheers guys - thanks for the responses...
Like reeac the handles on these are knackered ,so even if I successfully clean and rebuild I'll still have to find new - that alone is enough to make me think I'll buy new stop cocks - at this size they're only a tenner each and DZR as well...
Biljratt - the boat is 60's, but these are not original - I reckon they've been replaced in the last 10 years or so so probably off the shelves of B&Q..
I'll take the opportunity to replace the hoses and double up the clips at the same time..