I bought new weatherstrip for my front 2 doors. They were long overdue. The old ones were torn and very worn and let water and even dust in too easily. I got them from AMAutoPart, they were about $30 per door. Now I just need to do one of my middle doors but that will wait...
Old, torn weatherstripping:
Silver Sharpie to mark the cut:
The cut end, notice the metal lining and the pre-applied 'goop' that is used to stick to the metal.
Due to the metal being in the weatherstripping I found the easiest way to cut it was with a 4.5 angle grinder with a cut-off wheel.
Also buy an air freshener, the new weatherstripping stinks for a while