Don't use WD-40. It is more of a solvent than a lubricant. WD-40 only lubricates temporarily until pretty much all of it evaporates away in a week or so. WD-40 will dissolve what little grease you already have. The only idea I have is to disassemble the squeaky part and to lubricate it with a water
resistant grease, something like wheel bearing grease for boat trailers.
Pack what grease you can in there but if the bearing is sealed and it is squeaking it may need to be replaced. You definitely don't want your helm
wheels bearing to fail, I know that's really obvious.