Some Ford Mustangs with manual transmissions may require a specific Mercon-type fluid, such as Mercon LV, Mercon V, or Mercon ULV, depending on the model year and transmission. Others may require a specific SAE-rated gear oil, such as SAE 75W-90 or SAE 80W-90.
The owner's manual or repair manual for your specific Mustang model will provide the exact type and specification of transmission fluid required for your vehicle's manual transmission. It's important to use the recommended transmission fluid to ensure proper lubrication, smooth shifting, and optimal performance of your manual transmission.