Update today...

Mercedes service tech at my local dealer says to tow it in so that they can take a look. He says that he's seen this before and Mercedes has covered the cost of the repair as long as it looks like the owner wasn't negligent in any way. (How can someone neglect the undercarriage weld point of the spring??!?)

So I'm fairly encouraged that they'll take care of the fix but I'm sure there will be a catch.