[Tim Brewer]

It's really hard to fix a pinhole, the inside of the area around the pinhole is probably rusted too thin to weld shut. You may have to have a larger patch cut out and replaced and then the you'll have to have your whole pipe stripped and recoated. Annother thing to think about is if you had one weak area, there's a good chance you may have annother one as well that could pop up after all your repair work is compleated. So, if the pinhole is in the collector, you might consider changing out the collector to avoid doing a second repair down the road.