Got a leak in my valley (or should that be leek?). And I'm pretty sure I've
found the cause -a small 10 cm horizontal tear across the final sheet. I
think it's the cause because some silicon sealant roughly squished in on the
end of a stick leaning out of my velux does reduce the drip in the attic. So
on the next dry day if I stick a length of flash banding down the valley
will this stick for a few weeks so that I can plan my next move? Or is there
some better solution that someone could suggest?

Alistair in very rainy Manchester