Ok, thanks all for your replies and the warm welcome
Seems I should bite the bullet and send mine in for service. Unfortunately, my purchase is longer than 2 weeks ago, so I can't simply send it back to the online retailer where I bought it. Oh well.
I got this lens a few weeks ago, and I'm not really sure if I got a "good" copy or not. I do not notice any image quality flaws (no decentering etc.), but there is noticable wobble when I extend the lens all the way to 80mm, and during autofocus at 80mm, the image jumps slightly in the vie...