In my case, I've noticed that when I wax the car, wax simply clogs the hole of the opening of the jet.
I just take a sewing needle or clothes pin and clean in out. Then I run the jets for good measure.
Your owners manual I think shows a picture of where the jets should hit the windshield.
I think the dealers use metal rods that they use to aim the jets, but with simple trial and error, you can aim them where they should go.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".