During the years I have made it a habit of changing the wheel bearings every year on all my bikes no matter if I got them brand new or used. I have had a rear wheel bearing fail on me once and it totally destroyed the entire hub. Costing me several hours of work to replace the hub. When it happened I had checked the bearings when I changed tires just a couple of riding hours before it happened and they all seemed fine. So I learned the hard way that when bearings fail they can fail so fast that you will not notice it until it's too late. And I might add that that particular bike was less than a year old and with me as the first and only owner.
|Fill the gap with grease and your bearings will live longer|
If we go back to fact that bearings can fail fast it should be obvious that I will never go to a rally without having brand new wheel bearings on. Most manufacturers have wheel repair kits that contains all bearings, seals and spacers that you'll need and they are relatively cheap and it's quite an easy operation to change them. So changing my wheel bearings is an easy insurance that my bike will take me through deserts and rivers for thousands of kilometers without any troubles.