Hi, I've recently moved into a house that has windows in various states of repair. The frames are wooden and are beaded externally. Some of the older units have misted and need replacing. It appears that someone has tried to replace (badly) some units previously but with thinner glass, this is now loose in the frames and I can feel gaps between the glass and the beading. I want to replace/repair these myself but before I order new units a stupid question. Without taking the old glass out first, where should I measure to to order the new units? To the edge of the beading nearest the frame and what gap should I allow? I was going to use glazing tape and then replace the beading with some new stuff.