Replacement nut for RGRTBB21?

The stock nut has worn inconsistently where different string gauges have been used and now I suspect it's causing tuning instability. Anyone have any experience swapping out the nut one of these? Recommended materials? DIY-able or have it done by a luthier?

The stock nut has worn inconsistently where different string gauges have been used and now I suspect it's causing tuning instability. Anyone have any experience swapping out the nut one of these? Recommended materials? DIY-able or have it done by a luthier?