FORD 2008 Mustang v.2 - Manual (Page 268)

Use of a non-approved automatic transmission fluid may cause
internal transmission component damage and void the warranty.
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. Note: There are two different manual transmissions used in this
vehicle and they have different fluid levels. For vehicles equipped with a
V6 engine the correct manual transmission fill level is at the lower edge
of the filler hole. For vehicles equipped with a V8 engine the correct
manual transmission fill level is 1/2 inch (1.3 cm) below the edge of the
filler hole.
2008 05+ Mustang (197)
Owners Guide (post-2002-fmt)
USA (fus)
Maintenance and Specifications
268