They will eventually go bad. It will be the vac hoses that will cause the problem. Kia fixed the hub seal part back in 1999/2000. You also need to make sure the front wheel bearings are adjusted properly at all times OR sometimes the new vac seal will also not hold the vac.

Overall they are OK for street use but for serious off road I would get the warn manual/OR automatic hub kit for your Kia. The guys on the board here have a lot of experience with the hubs. Do a search and you will find many posts.