Thanks for all the replies, y'all. It's been rainy and my parking spot isn't paved, so I haven't had a chance to look at it.

I've been paying closer attention to it while driving the last few days, and I would say that it isn't so much a constant waver in steering direction as it is an intermittent, sudden slight pull one direction or the other. It's not the lateral scoot that happens when rear links are bad, I've felt that, it's definitely a steering motion. Also, when I let go of the wheel, it tends to track straight for a good while, then it will tic slightly one way or the other. The problem disappears completely in turns, I assume because the steering system is being "snugged up" so to speak by the lateral force on the wheels.

I don't know if any of this helps diagnostically, but I'm always mindful of people finding my posts years down the road so I like to be as thorough as possible!

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RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)