From yrragnwad
Yes they can be repaired, the sagging nags head only takes a few minutes to stiffen up, I have done loads in the past.
It's another hot water method, hold the horses body in one hand get hold of the nags head ( nice pub just down the road) & pull it off backwards towards the horses body.
You should of course put the kettle on first, one cup for your tea & one cup of hot water for the horse. Don't put the horse into boiling hot water, let it stand for a few minutes you only want too warm the plastic up. If you put a black horse straight into hot water it sort of bleaches it & sends it greyish.
All you need to do is put the neck part into the water & leave it too warm up, give it a 3 - 5 minutes, take it out & then just squeeze the 2 neck sides inwards using gentle preasure, you don't want too close the gap just reduce it by about 1mm.
On the horses head you will notice two round raised parts either side on the bottom, these need to be located into the 2 grooves one either side on the neck slot of the horse, with the head held in an up position just push it back in until the two lumps click into the inside part of the holes you see on either side off the horse.
Test it for stiffness if it's still loose do it again, eventually you will get it right every time first time with practice