I like the ATF/Acetone method. It works, but is somewhat slow. For a more aggressive method (quicker acting), you could try a little D2 or Kero on the metal to rubber location(s). It creeps and helps dissolve/loosen the metal/rust to rubber bond. Learned this trick years ago when busting tractor tires in the field. Gasoline really works well BUT its very tricky & very aggressive, not to mention very flammable. Ditto for volatile solvents.

Oh yeah, almost forgot - Fire Safety First! Heat &/or flame and solvents do not mix!!