Help: SRAM brake levers keep slipping

I love the SRAM carbon brake levers, but the darn things keep twisting in the basebar.
I’ve tried tightening the expander(I mean REALLY crankin’ it tight), scraping the inside with sandpaper, and even epoxying them in.
The epoxy didn’t hold.
Anyone have the same problem? How did you fix it??

My next attempt will be to put a piece of tube inbetween the expander and basebar.

FYI I’m using the easton deltaforce carbon basebar.

is the actual expander mechanism for the levers AL or carbon ?