Do you have a downavator that is just missing the pin that connects the piston to the linkage? You could use a lego axle but a 3D printed part works too!
You may want to try printing vertically with a brim. I think printing horizontally will make a stronger part given the direction of they layer lines. Might need a bit of support material if it isn't sticking to the print surface well.
The author hasn't provided the model origin yet.