thanks all for the advice, i phoned paul tilley of TIDEL today as he was reccomended to me by a 'boaty' bloke i know. what a great bloke, freely gave advice and obviously knows his stuff inside out.
yep, start with soapy water, around the old patch, the valves and seams etc. get a lapdancer or two to help iff poss !
then take it from there, it could also be behind the rubbing strake which i hadnt thought of.
Once i find it if it needs 'proper' attention its going to TIDEL, close enough to me to make it the easy option.
thanks again, i'll post a follow up once i fix it!