yeah..... Front pinion seal. Remove shaft completely, remove pinion flange(believe its a 32mm socket or a 1 1/4 or 1 1/8), pull out old seal, gently hammer new one in, slide on flange and buzz on nut, done. If you dont have an impact, dont even try. Nuts on there very very tight.

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'01 XLT disguised as a '03 Fx4 Level II.