Just my 2 cents.
I have seen cars go 100k and never have the bearings packed – checked.
Problems, sometimes, most of the time no.
Grease that is caked solid when taken apart was usually on vehicles that had many miles, many years, or over heated or just plain garbage grease was put in when they were repacked.
I think if you do it right, every year is a little much, especially with the greaseable hubs, providing you do that correctly.
Spinning the wheel does two things. Allows the grease to be distributed around the rollers. Helps push old grease through the rollers and takes the load off the bearing so that you can actually get the grease around the rollers. If you are not spinning the hub when you are pumping grease in you are wasting your time.
Repacking, if you do it correctly, gives you the opportunity to physically look at the bearings to see the condition. I’m assuming that if you have the instinct to actually take all this apart, make a mess cleaning and repacking then you have the ability to look at the bearing and judge condition.
BTW, if there is even a single spot on the roller that looks iffy (might look like a pit or flaking) change all the bearings.
If you are taking apart the bearings to do a hand repacking – how are you going to clean them? How are you going to repack them?
Always use new seals, double lip with a spring are usually better seals, single lip or no spring might be a sign of quality.
Buy good grease, stay away from HF stuff.
Now if you are inclined to go to a shop to have it done be aware there are two ways to do it, the right way and …………………………
This is from over 20 years in the automotive field, little over 18 at new car dealers as a class A tech.
I have done scores of bearings over the years and never short changed the job, never made a lot of hours either. Use to tell my trainees that “there is never enough time to do the job right the first time but there is always time to do it right the second time”. They would give you that bewildered look and then I would have to explain - do it right the first time.
I have seen on many occasions short cuts on bearing re-packs. Conscientious customer comes in and wants his bearings repacked. Pays his 2-3 hour bill and drives away happy that he had proper maintenance done, little did he know all the “tech” did was pop the cover and put some grease in the cap.
It is buyer beware for even the simple maintenance.