a quick fix if your grey coupling got loose or even squeezed out between the wooden parts...
it's tested on two ultimakers and works niclely.
This thing was made with Tinkercad. Edit it online https://tinkercad.com/things/2oH8KCdCJ7O
The block fits firmly over on the quick fit coupling and the two wooden plates.
secure it with 4 small screws and it will hold like a rock.
it's also not intervening with the cupling's horsshoe or the delrin handle.
it's tested on two ultimakers and works nicely.