There are more severe measures available from both Meguiar's and 3M. I will look up the numbers and terminology if you are still interested. Offhand I seem to remember there being 3 "levels" beyond the #9 phase. The most aggressive being one step above wet sanding.... Not to be done lightly but if all else fails. Give the clay a try first. BTW Meguiar's clay is too soft to work on most stuff. Clay Magic works much better but use #34 or Slick Stuff as the spray lubricant.

Best of Luck...Lee