Damp patches in bottom corners of a double glazed window after rain

I have noticed two damp patches on the plaster in the bottom corners of a double glazed window - they are on the plaster at the side of the window, as opposed to the window ledge. The window itself seems ok, I wonder if it is a sealant problem? Is this a job for a glazier/windows, or should I be asking a general tradesman? I want it sorted so that I can repaint the area. Thanks