Short answer: Could be any of those things you mentioned.

Longer answer: You can start by checking the play in the steering while stationary. Park the car and leave the engine running. Then see how far you can move the steering wheel in each direction before the left front wheel starts to move. The CDL limit is two inches, but less is better.

Next, you can jack up and properly support the vehicle and start trying to wiggle the front wheels while they're in the air. With the steering column unlocked, you should be able to smoothly move the entire steering assembly with considerable effort and with little (almost no) play. If you notice some play doing this test, you can start at the wheel and work you way along the steering components until you determine where the play is coming from. It helps to have a helper for this one. If you have excessive play in the first test, but don't find anything in the second, you should try adjusting your steering box. It's also possible, but unlikely at your mileage, that you steering box is worn out.

If the car passes the first two tests, but feels squirrely on the highway, try swapping your front and rear tires and see if that changes anything. Also make sure that all tires are properly inflated, and while you're doing that check for any sign of unusual tire wear.

That should be enough to get you started.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.