You say the seal was replaced and it still leaks. You talk about a scratch on the yoke, do you mean a cut all the way around where the seal rides?

I do not know what rear end you have, as you did not say. So I will guess it to be an 8.8.
If so this is an easy job if you have the tools, if you do not have the tools it is impossible for you to get it right.

First you have to find a way to hold the yoke from turning, not an easy thing to do. I cut out a tool from 1/4" plate with my cutting torch 4 ft. long that bolts to the yoke with a hole for the nut to come out and go in through.

Second you take the nut off with a 3/4" ratchet with a 4' pipe on it. Some say they get away with an impact wrench here but if you do you might do the bearings in.

Third mark the position of the yoke to the shaft and then you pull the yoke off with a puller.

Fourth pry out the seal and take out the crush sleeve.

Fifth put in a new crush sleeve, drive on the seal and put the yoke back on in the same position that it was before you took it off unless you are replacing it. You did mark it did you not?

Put your holder in position and tighten the NEW nut to about 12 to 14 inch lb. with your 3/4" ratchet and 4' pipe. If you go over 14 inch lbs. replace the seal and crush sleeve and start over. You can not back the nut off.

The 12 to 14 inch lbs. is how much it takes to turn the yoke with the drums off using a 40 inch lb. torque wrench on the nut with used bearings. KD tools sell the torque wrench.