So, from searching here, I knew to look at my sealing rings.

This is what I found when I opened my hood:



Probably drove quite a few miles like this before I noticed it. Glad it didn't fall out of the engine bay. The clamps were super loose. Wrestled it back on, tightened the clamps and it seems to be happy.

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1998 E300 +310,000K
1996 E300 +460,000K

Unless you were driving on a dirt road at the time, you should be fine.