wd40 will just evaporate and offer only temporary protection.

you already got the answer right here in the thread, RUST CONVERTER. meron nyan sa hardware like wilcon or handyman, o kahit sa ordinary hardware stores. ask mo lang rust converter. one of the popular brands is OSPHO RUST CONVERTER. chip mo lang ng konti yung rust pag masyado na makapal pero pag manipis lang naman hindi na needed i-chipping. apply a liberal amount of the rust comverter and wait maybe 1 hour. the rust will turn black in color. the iron oxide (rust. FeO2) becomes converted to ferous sulphate (FeSO3) which is a very hard, anti rust coating. huwag mo na gagalawin pag naging black na kasi yung black coating na yun ang mag-prevent ng rust. wash with plain water after. tapos na wala ka na problema sa rust.