Repairing cracked lead valley flashing

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Woke up two days ago to find water dripping down the wall of the spare room. After a bit of investigation (boiler above was originally prime suspect), we found the wood beam supporting the dormer valley to be soaked, and a roofer confirmed there a crack running across the lead flashing half way down the valley. Valley itself is done in a single piece of lead, but is probably not much longer than 1.5m. Think the synthetic slate roof was redone 20 odd years ago before we moved in, so in reasonable nick.

so far I’ve had three people to quote and three different options (four if you include complete replacement)

a) paint on some sort of roofing sealant paint down the full length of the valley (that’s a no from me ..)
b) weld a patch over the crack
c) flash band it

No-one had proposed a sleeve (if I understand it - take off a few tiles around the crack, cut the lead and add a piece under/over, then replace tiles). Looks great solution to me, but I’m just a you-tube warrior, so what do I know!

So far c) is by far the cheapest quote, as he can do it without scaffolding - it can also be done quick, and there’s a lot of rain forecast. I’m having to manage the situation with towels in the loft, as there’s no drip I can catch - so that’s a factor.

advice ? I’ve got one more person coming round later, what would you recommend I ask?
 
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Ok - last guy has also proposed liquid polymer paint (or full replacement).
 
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The flashing tape will stop the leak, IF the problem is the broken valley. I have used this before, but I would regard this as temperary. Beter you at least put a repair patch of lead in the bridge the break.
Or do you have compo breakout under the tiles and the water is gushing in that way?
 
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Thanks. I managed to take off all the kingspan (question for another thread) and see where the water saturation on the board below started - one of the roofers tapped from the inside when his mate was up there, and it matched up to where the crack in the lead was. So fingers crossed it’s just that and not another problem.
 
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If it is 1.5 or less there are two possible causes for failure .
1 wrong code lead 2 wrongly fixed lead.
Painting it is a waste of your money and will only delay what you have to do.
Putting a piece under the crack would work if the remaining lead is of the correct code, which I doubt.
Strip out , and replace is the sensible option .
 
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Thanks - here’s a picture,
BDF10DB4-EC60-44DE-B8CC-70B4CF4BA21F.jpeg
you can see the horizontal crack about half way down.
 
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