Just adding on. I had the same problem on my 2004. The wiper was barely touching the glass. It used to work fine. Replacing the rubber insert did not help.
But after taking off the cover (that covers the nut that holds the entire wiper on) I noticed that the blade arm had split on one side of the attachment point over the motor spline. So the wiper still moved back and forth, but did not have the right angle anymore.
I am just adding that the metal grommet inside the plastic arm that slides on the motor spline was totally rusted on. The plastic arm just fell apart and all I was left with was the motor spline with the metal grommet fused on it. PBlaster did not loosen it and I did not want to torque it too hard with pliers.
But the earlier references to a puller helped. I ended up going to Autozone as they will lend out tools for free as long as you return them. I picked up a three arm puller. With some work, it popped off the rusted grommet. With some cleaning solution and a small wire brush I cleaned off the spline and it looks good to go while I wait for the replacement. I did put a light coat of oil on after cleaning so the spline remains rust free while I wait for the replacement. Here are some basic photos.

Here is the cleaned off motor spline. Note that the spline part is tapered. The threaded part is where the nut goes to hold on the wiper.

The puller may have a point on tip the bolt you tighten, but it was easier to put the wiper arm nut back on a few turns and rest puller bolt in the natural cup this creates. Note that the nut is not tightened down right to the spline. This leaves a bit of room for the wiper grommet to pop off. But make sure to tighten the bolt enough so there are a few threads for support. You just want a small space for the grommet to pop off the spline. That's all you need as the spline is tapered. Once it pops you can easily remove it by hand.

Here is the actual metal grommet that was embedded in the plastic arm. Yes, it is a bit chewed up as I gently tried using wrenches to remove it. It rests on the tapered spline in the front of the tapered spline right next to the threads. It does not go all the way back. But note how small it is. The puller worked well, but I had to rotate it a few times to get the best grip behind this grommet.
Lastly, a few more comments for those in this situation.
- Hold the three arms of the puller with your dominant hand. You may need the strength to keep the arms on and behind the grommet.
- Slowly turn the puller bolt with your wrench. Going too fast just makes the arms pop off
- You may need to turn the puller at times to find the best edge for gripping. My truck is 11 years old so the metal grommet was pretty bad.
Keep in mind that in my situation the washer arm was already broken so I just busted it off to expose the metal grommet. If you are trying to save the arm you may have a lot of difficulty if it is rusted on. In the end you may just decide to get a new arm. I found an OEM replacement on Ebay for 34 bucks delivered. It shows up this week and I will pop it right on.