Harley had a recall with the 06 dyna's regarding your problem. The fix is a thicker washer under the steering head nut. Any Harley shop should have the washer in stock and it's a easy fix with the right tools. I can't remember the size the the steering head nut been too many years since I sold my 06 superglide.

do you have floating discs ? they like a bit of heat in them to sit right