If you must use your wipers, you are mistreating your Porsche. It should never be left out in or driven in the rain. My boxster's windshield wipers have only been used twice, and I went straight to confession afterwards
She's old and beat up, but she's a garage queen now!
I put some Bosch replacement wiper blades/bows on the car and it cleans the windows beautifully. Don't replace just the rubber bit.