So my freehub has gave up and seems a straight forward job in replacing it. Only question is & basic but is there a specific shimano hub needed to replace it or can a generic one less expensive available
I’m sorry to say that you will have to get one designed for your hub, cheap ones for other makes won’t fit. However, I wouldn’t mind betting that it is the outside sealed bearing which has died (speaking from experience). Try tapping the bearing out with a small hammer and screwdriver and see how it feels, it is a readily available bearing which costs about £5. Carefully tap the new bearing back in but don’t forget the spacer or you will have to strip it back down.