egruber,
The toothbrush/soap technique works well in some situations. As does applying any other kind of product stripper. You can even try applying some Meguiar's #7 then removing with a terry. Or using the technique above, apply the #7, then remove with toothbrush.

For rubber conditioning I like either the Meguiar's rubber/vinyl dressing or Vinylex by Lexol.

Hope this helps..>Lee