Just a stupid ?. If the seal doesn"t leak, where does the grease go. A high quality grease should be there forever. My car is approching 100k and I just had brakes done and I told mechanic to change bearings/seals if needed. He did not think any service at this time.In 2009 I changed my brakes to disc and new wheel bearings and seals ( came as part of a kit) have not been touched since and inspection says they are good to go. Dexter says yearly. I say every time you pull the wheel to inspect the drum brakes. Which I believe you should do but I don't have that problem so I elect to leaave well enough alone.