You should repack your bearing's with grease at least once a year.jack wheels up,spin wheels,listen for rumbling,if all good then, pull bearings out,wash out with petrol and a paint rush,rince with water,blow dry if you have a compressor, inspect the rollers and case hardening for flaking if no flaking or corrosion or pits in rollers or roller track then repack them,and reuse them,no use changing bearings for the sake of it.put new seals in.