Ford 2003 Mustang Workshop Manual page 2840

52. Install the shift spring and bracket.
53. Install a new split pin in the gear shift off-set lever.
The split pin should be flush in the gear shift off-set lever.
54. Seat the extension housing and tighten the bolts to specification.
Fill the gear shift off-set lever with petroleum jelly.
55. Using the special tool, install a new extension housing seal.
Lubricate the seal with transmission fluid.