Hundested variable pitch prop slipping

[Marire]

Hey everyone,
We are looking for some advice on our Hundested type FR variable pitch propeller.
The prop has started slipping, and will not give any thrust. I've dived under the boat, and removed the three blades, in an attempt to strip it apart to find out what is wrong.
With the gearbox in gear, the prop shaft (inside boat) will rotate freely one way, and lock the other. However, when I spin the prop by hand under the boat, it rotates freely in both directions.
Do these types of prop have a key and key way? It feels to me as if the key may have dropped out? Otherwise, I guess we are looking at a broken shaft? It doesn't feel rough when I rotate it by hand, which to me doesn't suggest a breakage?
I'd really like some drawings for the unit, but am unable to find anything convincing on a Google search. I'd also like to know if this prop has a key, and if so- what size it would be, so I can obtain one ready for the dry dock.
Finally, I've never removed a prop before, and I'm not even sure how this prop would be removed from the shaft? Does anyone have any experience with these?

Any help is much appreciated!!
Kind regards,
James

[Marire]

Here is a photo showing the prop with blades removed from underwater

[Marire]

And here is a photo of the FR unit. (Sorry it will only let me add one photo at a time)