had a failure of one last year while towing. Failure also ruined the spindle so even if i had a spare unit i could not have used it. Also, the failure allowed the wheel to cock on the axle causing the tire to rub against the shock mount destroying the inner side wall of the tire. After that i would not do 'never-lube' bearings again. If you have a trailer with them on already i would have them replaced periodically, probably at least every 2 yr. Before we bought the trailer i questioned the practicality of the 'never-lube' setup & was told that very few failures have occurred which sounded good until i was one of the failures :(