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If you are talking about the side yokes, then the only way to remove the c-clips is to remove the rear cover of the differential to access the splined ends of the side yokes. Then it is a simple process to remove the old seals and put in new ones. If you're referring to the front seal, then you have to remove the large pinion nut and the pinion flange to get to the seal. The problem there is if you over-tighten the pinion nut upon re-assembly. You will crush the "crush sleeve" too much and have reset the pinion to mesh properly with the ring gear.
I did mine by grinding a witness mark on the nut and pinion, then lined the marks back up when I put it back together. That is not the best way to do it, but it worked fine for me, and the rear end of my car continues to operate without issue (or leaks!).
Gary (gtr99) was a great help, but I think he is no longer on this forum. It is very important to use the proper sealants when replacing the seals, or they will leak. Use black rtv on the seal housings (the part that contacts the rear end case) and use Permatex No. 2 on the splines of pinion flange or oil will leak past the pinion nut. Also pack the back of the seals with high temp grease before you install them so the circular springs won't dislodge when you're pressing in the seals. Also, use red thread locker on the pinion nut.
There is a young guy on the forum (Stinger something or other). He has a great thread on rebuilding his diff that covers this stuff in depth.