ditto on the boar bristle brush. seems to stimulate oil. and the acv. i have to use very, very little, maybe 2 tbsp in a pint of water.
try this if you don't want to ditch the eo's. wash, use acv & water, rinse. put eo's in widemouth jar/bowl. add shower water. dip the *length* of your hair in. then pour remaining water over your head. this way most of the eo's should cling to the length of your hair away from your scalp.
but i understood eo's to be different from carrier oils anyway, in that they absorb into your skin very quickly, and shouldn't stick around to make your scalp greasy. you're only using a few drops right?
anyway, if you can't solve it & can't stand it, it shouldn't *hurt* your hair to use the bs as often as you feel the need. i just personally believe that less is more kwim?
just looked at your post again & it really sounds like it's the vinegar.