Well i finally got motivated and found my leak, i'll do a walkthough for those of you with the same problem - its caused by some an old rubber seal that seals no more
step 1 - remove your wipers, 1 x 14mm bolt on each wiper arm then wiggle (probably with the bonnet down and wipers up so the spring doesn't push anything
step 2 - flick out the 3 plastic plugs recessed into the plastic panel under the wipers
step 3 - pull the rubber seal off that runs across the back of the engine bay, tool of choice would be the needle nosed pliers with a bend in them as the rubber is held in with clips that can be pried off but can also be squeezed from underneath (that way they don't break)
step 4 - pull the plastic panel out to reveal your wiper mechanism and the base of the windscreen, you can now access the offending part
Here it is:
pull it out and it doesn't look so good underneath
the rubber has perished
clean everything up and apply some gasket goo
reinstall and reassemble and hope its all good
I de-greased and wd40'd my wiper linkages, now my aircon smells like wd40 -> a word of warning if you are thinking about going nuts with the wd40