I tried this tip on mine today, and it helped a little, yet I only added about 1.5mm(used a cone washer for a 2mm screw). I think the the amount of toe out and castor also affect the amount of bumpsteer. Basically the two pillow balls and the steering link on the hub want to travel up and down in the same parallel plane. This topic was brought up in the MBX-6 thread, I don't recall if anything was done to the link at the ackerman as well.