So further exploration showed the high-beam still working, so I bought a $20 Sylvania XtraVision H7, tried to insert in the dark, and decided that was dumb. So I stopped.
I'll try again at some point when I can see and it ain't deluging rain and/or snow.
Last tank Shell premium once again 24.9MPG. Either the formulation has changed for the season or those 80--110MPH extended runs and heavy dirt-dancing are catching up to me

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