Looks like I have a worsening leak witht the air valve that sits on top of the filter. It is part 2 in the diagram. It will allow water to pass even when closed and still sounds like air escaping-strange.
Is it a simple matter to unscrew this piece and replace it? Pool store says they have a replacement piece although it doesn't look 'exactly' the same, I would guess just a newer version. My fear is something will crack or break and I need to buy a new filter.