You should be able to reuse the seal on the Diff
If You replace the Yoke please make sure that the Yoke is Clean
with NO Scratches / ridges to avoid a leak..Clean it with very fine sand paper..if any scratches...
Also Be VERY careful when Installing the Yoke..NOT to knock off the spring on the seal...If the spring is Knocked off You WILL have a Leak!
The Seal is NOT a big job to replace with the yoke removed!