i had the same problem. it was fast sometimes and then somedays, it would slow down to a crawl while wiping across. I too was quoted a grand to repair/replace the wiper motor. all you need to do is LUBRICATE the arm that extends up and down.

I didn't even have to remove that big black piece in the middle. You can do that it way as well. What i did was turn on the wiper till it's in the straight up position and then shut off the power. Now, remove the little black piece that's above the big circular black plastic piece. It just pops on and off. After that, you'll see a hydraulic arm that extends in and out. I took some household oil and lubed it. Works great ever since.

Voila, you saved yourself $1000!