All of the things suggested can contribute to this problem, but in almost all cases severe wobble as described will stop if the swivel preload is right, and fixing everything else will not stop it if swivel preload is inadequate.
In a vehicle with that mileage there is a good chance that there are a lot of contributors to the problem, but I would have started with wheel balance and then swivel preload. Most of the other contributors to the problem will show other symptoms as well (which may have appeared unnoticed as they start gradually) such as wandering steering (bushes, tie rod ends) or brake pad knock back (wheel bearings).
John

