Start with the simple yet often overlooked items, check the front axle nut and make sure it is tight and the front tire spins freely and straight when off the ground. Next, check air pressure in your tire and the front forks for any sign of fluid leak from the seals. If still no luck finding any cause then move up the forks and check the lower and upper tripple tree Allen bolts and make sure them things are nice and tight. If so done did the Fubur fix then a possible loose clamp on the tree could be the cause. If still nothing and you have the time and tools, Allen wrench and a large crescent then loosen the lower tree clamps and if needed tighten the steering head bearings. It should be tight but still allow your steering to move freely without bouncing off the stops. Once tight remember to retighten the lower clamp bolts. If after all of this and nothing stands out as being bad, worn, loose or just wrong and the problem still persists on your check ride I would guess that your steering head bearings need to be replaced.