Do I need a new seal on my differential?

What should I do my differential case on my 99 ford f150 xl 4.6 liter is half normal color and well you see in the pic. What should I do

What pic?
If you are talking about this pic: http://www.ford-trucks.com/forums/attachment.php?attachmentid=58235&stc=1&d=1342882996

You are going to need more than a seal.

What pic?

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