Using Rubber Roofing For A Valley?

Had an extension built about 12 years ago, builder put the lead roofing valley on flat with one piece of 20 foot lead for the valley. You can guess what happened, valley is taking water from 3 roofs next door , ours and the front roof. Been thinking of ripping it all off and making a 4 section staircase to take 4 pieces of 1.5m approx lead......snag is we have 2 smaller lead valleys taking the water from the front roof so we cannot really lift the valley at the roof end...
I was wondering if we could remove the valley lead and put small fillets onto the bottom valley board to give a slight run off and then bond this rubber EPDM roofing onto the clean wooden valley?
Any thoughts, any other options?
Rob

I have not used the rubber stuff but if its waterproof then I don't see why it won't work, another option is ubiflex which resists expansion fatigue.

EPDM is excellent for valleys and box gutters as long as you are properly glueing it to new fresh timber and using off cuts of rubber to protect the 1st layer from tiles resting on it over the years.

Use GRP dry valleys, they're the biz.
They are almost invisible once both sides of the valley tiles are cut up and despite what lead purists may tell you, they are about as degradable as nuclear waste.

I think he means a flat valley, taking several roof pitches.

Rubbers perfectly okay, if the budget allows use Resitrix.