Certainly check the wear on your tires. If there is asymmetric wear (outside wears more than in for example) your tires could be "toed in" to suggest you need an alignment. Good start with having your tires balanced.
Could also be the rubber bushings and brackets in the steering apparatus.
Make sure they're situated firmly.
...stupid question but you've made sure your tires have appropriate PSI in them, right?

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1987 300e W124 M103 My baby.