My new roof was installed about 8 1/2 years ago. All new plywood decking and Certainteed Presidential line 50 year composition shingles. The plumbing pipe vents were flashed with Award Metals flashing that appears to be a type of galvanized metal with a rubber-like bell cap that slipped over the vent pipe. The label impressed on the metal flashing says "Award Metals" and a magnet stuck to it, so I assume it is galvanized metal of some sort. This vent pipe flashing is 12 1/2 inches wide, and I estimate about 14 inches long (the upper part is hidden under the shingles). Now, after only 8 1/2 years the rubber-like bells on the flashing are cracking and separating. I can't find any information on warranty for the flashing on Award's web site or in their product documents. Is this normal, expected behavior? Replacing the flashing would require ripping up quite a few shingles on an otherwise fine roof (there are 5 such vents and flashings on my roof). How long should such flashing last (I live in the Portland, Oregon area)? What should I do to remedy the situation?
Sorry I couldn't upload any images; every format I tried (png,gif, jpg) failed, even tho' in acceptable file sizes. Any advice on that would also be appreciated so I can upload them.