If you look carefully at the crown you will see that the teeth are not square to the axis, so you cannot substitute a standard crown. The effect of the off axis is that there is a sliding motion between the crown teeth and the pinion, and a vertical load on the axle. All these things tend to cause more losses and more noise. But if there is a small imperfection in a tooth on the crown then the effect is more pronounced than in a standard in line set up. To be honest I doubt that dressing will cure this, toothpaste may make it a little better but I would budget for a new crown.