Would you replace both the Steering Lock Assembly and or just the ignition lock tumbler for a 1983 Mercedes 300 SD that you have to jiggle the steering wheel to get the key to turn in the ignition?

Replace just the steering lock unit. The tumblers are old, and they need to be replaces. After replacing the lock, go to a locksmith, and have him re-key the doors to match your new ignition lock.