Just had a phone call off a long term customer. Apparantly there are loads of water marks and black bits on the cills. Soon as i got there noticed she had all new units because they use to be leaded. not new windows just the units. As i was cleaning did notice some of the rubber seals where loose. I imagine the water has got behind and run down the glass when ive come away. Going back tomorrow to sort it. Did give them an extra flush through as thought there might be a problem. I think this may be an on going thing so i will probably politely dump.