My problem is that the hub on my stern drive is responding fully to the throttle but the prop, although responding direction wise as if in neutral, won’t go into gear.
They're a sacrificial part designed to save the gearbox If the prop hits something,but they do just fail on their own sometimes. The prop will need to be removed and a new hub needs to be fitted.
Agree with @julians I had one go once. It was like a clutch failing on a car, lots of revs and little movement. I was in Croatia so bought a new prop but others will come on here I’m sure and suggest where to go for repair.
Get a price from castle for repair
I suspect there is also a lack of props available now from Volvo
sillete may have mor options without Volvo added tax