The detent comes from the spool valve moving far enough to seat a ball into a grove in the spool. This tells me your spool isnt moving far enough or the ball/spring isnt moving or is broken.
Have you inspected under the spool caps? They can get crud, water and rust under them.
Yes, and maybe I didn't mention but mine had no ball(s) inside at all. I carefully removed the cap and nothing came out. What remained on the valve assembly was the spool rod and spring. What remained inside the cap was what appeared to be a press fit ring about half way into the cap, with another spring below that in the end of the cap. No balls or anything. In that picture above you can see the end of the spool rod. It has a flat end, like you'd normally see on the top of an automotive shock so you can hold the rod with pliers while you tighten the nut or something. It's an odd design.
I found this exact part on the LS website, but the part numbers do not pop up ANYWHERE online for purchase. And the New Holland dealer swears that this part has been updated with a totally new design cap for the spool valve, and it has a list price of $400.
This is very frustrating.