Yeah it did fuck up rubber/neopreme/etc for the same reasons ethanol does. MTBE IS an oxygenate AND most certainly used as an anti-knock compound. It exists in higher octane gasolines for that reason. Other anti-knocks have come along which didn't have the health hazards and ethanol was something which offered up a number of plusses. Like everything else it had lots of drawbacks which we were happy to overlook for awhile. Right now its pretty fair with some exceptions.