FORD 2003 Mustang v.1 - Manual (Page 231)

An overfill condition of transmission fluid may
cause shift and/or engagement concerns and/or
possible damage.
Do not use supplemental transmission fluid
additives, treatments or cleaning agents. The use of
these materials may affect transmission operation
and result in damage to internal transmission
components.
Checking and adding manual transmission fluid
(if equipped)
1. Clean the filler plug.
2. Remove the filler
plug and inspect the
fluid level.
3. Fluid level should be
at bottom of the
opening.
4. Add enough fluid
through the filler
opening so that the
fluid level is at the
bottom of the opening.
5. Install and tighten the fill plug securely.
Use only fluid that meets Ford specifications. Refer
to Lubricant Specifications in this chapter.
Maintenance and Specifications
231