The underlying advance is to remove the old leaf and dirt. It is simpler if you apply linseed oil to the soil and hold for thirty minutes. You may also have the option of heating the dirt to facilitate drainage.
At this point, crowd out the fundamental interests of any glazier. You may need to break the glass to remove it. (There is a market in the craft world for extremely old corrugated glass, so you may need to try to keep it in a solid room or as huge as possible if it is the most prepared glass) .
By the time you have removed the glass and the rim is well scratched and away from all the old earth, it is a great idea to wipe the foamed linseed oil (you can also use light oil) on old wood. This prevents dry and dry wood from draining all the oil from the glazing, resulting in poor adhesion.