If you're using any type of windshield wiper fluid (the blue stuff or the orange stuff from Rain-X), about once a month, use a paper towel to wipe the rubber down with it. This will keep them pliable longer and increase their lifespan. I just put on my second set in almost two years, though. When I bought the Jeep, they were shot, so I got a set of double-blade wipers like I used to run on my Toyota. They really helped cut the mud off the windshield, but unfortunately were way too long. I could only find them as short as 16", and needed 11 or 12" ones. So, they wore out too quick from slapping over the top of the windshield frame. I went back to standard sized single blades this week, but we haven't had any rain, so I don't know how they'll work in the mud.
