I don't beleive it has ever worked, but I didn't even know what float detent was until a few weeks ago.
Perhaps I should have asked that a little differently:
Will the valve go into float?
Just FYI some older Kubota valves had a float position but the detent was a soft one. It provided a resistance point between pressure down and float but once the valve was moved past the detent into float it did not hold it there. I realize you may be perfectly happy with what you have but replacing that old valve with a new and fuller featured valve would be easy and relatively inexpensive.
Dan