I would try WD40 and a wire brush, several times until clean Once the major rust is gone try using ATF and then cleaning solvent to remove the ATF several times until it shines like new machining If it is pitted bad enough that you can feel the pits with your finger nails your to late
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Once the major rust is gone try using ATF and then cleaning solvent to remove the ATF several times until it shines like new machining 
