I really never considered a c-clip to be a maintenance item. There is really no wear on the c-clips so I don't see why you would need to ever change them.
The 10-bolt (c-clip axle) in my '90 had over 100,000 miles with no problems with the original c-clips. In fact, I had the internals completely rebuilt (4.10 gears, aftermarket limited slip, etc.) at about 75,000 miles and re-used the original c-clips.