For the last year and a half, or so, I've been trying to re-learn how to use koshi in my karate.
It's not that what I was doing before was wrong, it's just that what I was doing could be equated to gross motor skills vs. fine motor skills. Another way of thinking about it would be like the old shortwave radios that had a analog tuner that moved the dial around quickly between frequencies while another tuner was used to fine tune the frequency.
That's what I'm trying to do with my karate now...fine tune. Anyway, it took me 20 years to feel moderately successful with the gross motor movements, so I figure it will take me another 40 to get the fine tuning somewhat accomplished.
Check back here in about 20 years to see how it's going...