Use new, warm rubber!
Cut old rubber all around with razor knife & pop glass out.
Dish soap is good installation lube. Put new rubber on glass, & small cord in outer groove with cord ends hanging out together at bottom. Set in place on lower edge of cab opening, with as much of the "flange" in the groove as possible, and ends of string inside cab. Working slowly, pull cord out, which will spread open the rubber groove, and push glass/rubber onto flange as you go. Obviously, this is much easier with an extra pair of hands. Hopefully, it's all in place when you get around to the other end of the string!
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