I just picked up my "new" 2000 540i/6 last Monday, and it rained on the drive home. The passenger side wiper didn't move. I searched and read through all the previous posts on this, and figured I'd have a look at what might be my car's problem. What I found was that the splines on the inside of the passenger side pivot hub were all worn away. I removed the arm and filed new splines inside the hub with a small triangular file. I wasn't too hopeful that it would work, as I knew the "splines" I was making were never going to match. Anyway, since it was already stripped, I figured I would give it a shot. It worked! I put the arm back on, and tightened the nut, and away she goes.

I just thought I'd post this, because I hadn't seen it mentioned in any of the other wiper arm problem posts (plus I'm trying to get my post count up so I can post pics and urls).

BTW - I love the new car. A lot more oomph than my '86 325.

Yeah, it's happened before...same situation too. Dark and rainy on the interstate and the driver side quits. Sure makes it hard to drive!

The splines were worn out/off. I had read many moons earlier that new factory wiper arms had no splines at all, and the wiper post is what cut in fresh splines. So I filed out the inside of the arm and filed open the gap so I could tighten it up some more. It's been working great for about a year and a half so far. I don't expect it to come back. Yours should be fine too.

Before:
http://www.bimmerboard.com/members/zmuff/original/Wiper%20arm%20before.jpg

After:
http://www.bimmerboard.com/members/zmuff/original/Wiper%20arm%20after.jpg