as usual, doug is right. wd40 is a cleaning agent, NOT a repair. it will temporarily mask the problem. if you want to clean your jacks, feel free to use wd40. we do recommend wd40 for this purpose. it will also temporarily lubricate the cylinder and allow it to slide more freely, for a short time.
first, clean your springs. road grime or rust will cause springs to be much longer that they should be, and will affect retracting the jacks.
on the straight down cylinder, loosen the lower clamp very slightly, enough for the cylinder to turn within the collar,and try retracting the jack. if it will not retract, or retracts slowly, outside the allowed times published by hwh, you should consider replacing it.
if you have the new type of cylinder, that is held in by a lower clamp, and it is slow retracting, or will not retract, you can remove the lower clamp and file it out enough to remove the paint. it should not slide out of the ring milled into the jack cylinder. this cylinder is designed so that it should be able to turn inside the clamp, but not slide up and down.
if the clamp is too tight, it will egg shape the tube, and the shaft will not move freely. as ever, moderation and common sense should be used in filing the collar. do not over do it.