Dexter recommends clean, inspect and repack bearings every 12K miles or annually.
The quality of the grease is important . I use Lucas Red & Tacky grease.. My bearings are now 11 years old ( original factory bearings and brakes )..
Towing speed and weight also will affect the bearing grease and life of the bearings and races.
My latest video of what my bearings, races and brake shoes and hardware look like going on their 11th season of use..
** Some folks never repack, some folks insist in using the EZ lube zerk on the axle and call it good
Its a matter of choice
** I am old school, age 70, and too set in my old school ways of doing things to not pull the hubs once a year and put my eyes on what's behind the hubs..
https://youtu.be/W7ukKfZ15M0?si=pqPgpz33UyzzLCna