chagzuki

I've just phoned my nearest bike shops and I'm not convinced they know what they're doing, or that they're going to recommend the appropriate course of action. I've got an XRF5 which is fine in gears 1-4, but grinds in the fifth gear. I don't know much about the internals & how they work so I don't have much of an idea as to what could be wrong (it's not the cable length). One shop said that if any components need replacing they replace the entire hub as 'that's the way it's done'. ? I don't think so.

I know I'll find a decent bike shop further afield, but is this a job I could take on myself? With a clear tutorial I don't see that I'd have any problem unless specialist tools are needed, but I've not yet found any tutorials.