I've found some stations around LA, have just a crappier gas.
I try to use Chevron mostly.
My car had some weird problems, and I filled up at a station and they went away.
Filled up at another and they came back.
I would run some injector cleaner through your engine, and see if that helps out.
But I like the oxygenated theory you have, sounds like it could possibly be an answer. I am interested in finding this out too.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.