3 kinds of windows are out there, modern aluminum,vinyl,glass,,double pane
wood sash upper & lower puttied windows at the rabbets, ( angle of the joint where glass meets the window seam)
from the 60s back a hundred or two hundred years,,putty was used,,glass cut either on site, or in the shop,,,windows like these lasted 80 years needing only washing occasionally,some spots of dried putty replaced with fresh stuff,glass cleaned with rags warm water and pumice.
My apt in a 100 year brick 2 flat were all clean clean reputtied by me in ;92,,using daubs of linseed oil before bedding the glass in,a curved flat knife to smooth in the newputty brand I used.all wood surfaces cleaned with a belt sander, then painted a couple windows at a time,till all were done, heat insulation is still pretty good,sounds outside are muffled,,my ft door closes a bit hard because the space is sealed tight.
I must frankly redo about 3 northfacing windows because a leak upstairs caused putty deterioration.,,the old techniques worked well,as anon above says,,wood sashes puttied and properly treated last & last.
signs your window issue is an issue, drafts,,windows do not close all the way and close tightly,windows rattle when a door is opened,,that indicates weak air currents cause heat and coll air loss,besides eventually causing glass to crack,
noise from outside is more pronounced.
cracked glass,,sticky windows to raise and lower,to the point where a window breaks with a slam.