Besides the mast being slightly bent, you may also have worn or lightly stripped teeth on the plastic whip that coils up inside the mechanism. The whip is part of what gets replaced with a new mast. If you are very careful you may be able to streighten a lightly bent mast, but if the teeth are damaged you will need to replace the mast.
Lubrication does help and should be done once or twice a year as maintenance. It helps to use an assistant to turn the radio off and on so you can stay out with the mast as it goes up and down. With the mast fully extended, wipe the mast with a rag with WD40 on it. Leave the mast a little on the wet side and have the mast run down and up a few times and wipe it again. Repeat at least 1/2 dozen times. Finish by wiping most of the WD40 off the mast but leave it still very slighly damp.
