Well, I'm full of admiration for someone who fixes a problem so swiftly! In disgust at their bearing slackness, I packed away my Unimat milling heads and tried to forget about them. Perhaps motivation will now return…
When you had the quill apart, did you investigate whether a standard-sized ball bearing could be fitted into the nose end of the quill as well? Presumably, it would need to be bored out, as at t'other end.