Take a thin screw driver or flat cold chisel and gently tap it in the seam around the dust cap and hub working your way around until it comes off.
Some clean it well and apply a coating of silicon when putting them back on.
Just taking off the dust cap off to inspect won't do the trick. You need to remove the retaining nut and remove the hub for inspection and repacking. Don't forget new seals as well.
Linear Mode
