When my windshield wiper blades begin to leave water streaks I usually head up to Autozone for a new pair that they install for me or buy a new set and install them myself. A few months back I had a new thought, "should I try cleaning them first?". A little research led me to the link below and I followed their directions on cleaning them with isopropyl alcohol. As you can see in the picture below, I removed a lot of black gunk from the blades, and they now are back in good working order.
I wonder how many hundreds of dollars I've wasted over the years on prematurely replacing wiper blades. Probably best not to dwell on that.