Thank you everyone, specially for detailed information and advice, I have learned a lot.
I was not concerned about bearings and initially planed to buy cheaper ones, but your comments have changed my mind and I have just ordered the whole set for wheels and hub, brand Enduro, 2rs-llb-abec3. I believe it is a good investment, I will ride more confident and, hope, perform better. Also I expect they will last a long time and still using them following a proper maintenance.
The bearing in the picture was seized, the only one of all 6, but I believe it was faulty from the beginning because the rear wheel always sounded like a very light "clonk" when laterally shaken. I have recently learned that it is not normal and I am afraid the seller of the bike cheated on me. Let's see it the "clonk" is gone after assembling the wheel with the new bearings. That's the reason the bearing is so much damaged. I think the remaining bearings are still reusable although I will keep them just in case I have some emergency; they only have rolled 3700kms.
Last edited by patricio.montes; 01-30-19 at 01:11 PM.