Dear James: We have older wood windows, and some of the glass panes have cracks but are intact. What is the easiest and best method to replace the glass panes myself? —Denise K. Dear Denise: Replacing a glass pane in a wood window sash is not rocket science, but it is often done wrong. The glass pane may stay in place, but a do-it-yourself job is easy to notice. The putty lines are often not straight or even, and the paint usually gets over the glass pane. There are other potential long-term problems from a poor glass pane replacement project. If the wood surface, which the putty contacts, is not prepared properly initially, the putty can dry out and crack. The cracks allow moisture to get into the wood, which can damage the sash over time. The first step before removing the old broken glass from the window sash is …