Have you checked if there's any staining on the insulation itself? Sometimes drywall hides what's really going on behind it. I've seen leaks that look...

Yeah, visibility can be a real pain, especially on those darker shingles. I've had similar trouble with grease pencils fading into oblivion after just...

Haha, ghostly plumber... that's a new one. Could it be condensation building up around the vent? I've heard temperature differences can cause weird dr...