This weird dark brown stuff has just appeared on one of my rafters near the top of my roof by my chimney breast. I've had unfortunate luck with roofers and since 2012 it's leaked here, in fact I think it's been leaking (on occaision) in this place since before I bought the house 9 years ago. It only gets wet in the worst of weathers though.
Do you know what it is and do you know how to fix it?
It's too high up for me to get near BTW.