W,
It's hard to tell the condition of the internals untill you open it up. Of course if you have a ton of play, grinding or binding while rotating both axles or one at a time, then you have a problem.
The ring & pinion setting is only one of several renewable parts over hauled during a rebuild. All the seals should be replaced, the bearings inspected & the carrier thrust washers and planet gears fiber washer replaced. The bearings as well as the ring/pinion seem to hold up very well.
I have found that the "magic" Churchill case spreader is not required. The carrier can be pryed out gently with very little work.