i have a split level house, with two roofs at right angles to each other, one higher than the other. where the lower peak cuts into the slope of the upper roof, both valleys are leaking somewhere near the bottom of the valley or around where all the flashing from the higher roofs facia meets the slope of the lower roof. are there any good products for coating overtop of the existing asphalt shingles?? Or am I going to need to rip off the shingles int the leak area??