We have air bubbles coming through the inlet jets. They seem to come in spurts, stopping for a few seconds then another burst of them. It has been doing it since we opened the pool about a month ago. First we lubricated the o-ring on the strainer pot lid, then we replaced the o-ring, we also replaced the o-ring on the automatic clorinator lid. We don't know where else to look. Where are the most common places for an air leak and how do we diagnose the problem?? In case you need to know, its a vinyl in-ground pool with a challenger 1 1/2 hp pump, 9 years old.