Ford 2003 Mustang Workshop Manual page 338

18. CAUTION: If the rear axle drive pinion seal becomes misaligned during installation,
remove it and install a new one.
Position the rear axle drive pinion seal in the seal bore, and use the special tool to drive the seal
into place.
19. Lubricate the pinion flange splines.
Use SAE 80W-90 Premium Rear Axle Lubricant XY-80W90-QL or equivalent meeting
Ford specification WSP-M2C197-A.
20. NOTE: Disregard the index marks if installing a new pinion flange.
Position the pinion flange.
21. Using the special tools, install the pinion flange.