I would clean off the oil/grease everywhere you can reach (hand work mostly).
A hot pressure washer will do a fantastic job of finishing the degreasing process.
I would then use Ospho to treat the rust (encapsulating it).
Hit it with the pressure washer again to remove the white chalky Ospho residue (byproduct of the chemical process).
Paint with Rustoleum Rusty metal primer, and topcaot with Rustoleum semi-gloss black.
Carl
