ARW wrote:

On my Makita you could just swap the ball bearing.

Thanks for the thought. I did wonder about that, but I think there's more
amiss: previously, the outer sleeve was held out by some sort of spring
mechanism and it took some pressure to push it and (presumably) part of the
chuck down so the tool was fully home before I twisted it: now there doesn't
seem to be any resistance at all, nor anything which normally holds the
sleeve in its outermost position.