Acorn... In this case, I think ya did fine. Curled/peeling shinlges might be able to be fixed (hand-sealed), or they might need replacing. I agree, punt to the expert (yes, a roofer is, at least should be and is in many cases I've seen, an expert). This is (much) different, though, than say a cracked heat exchanger. Then I'd agree with Kurt's thought...why *evaluate* ? Just report the CO problem posed by same, and have the furnace replaced, now.