One problem related to transmission fluid leaking has been reported for the 2003 Ford Mustang. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Ford Mustang based on all problems reported for the 2003 Mustang.
Under heavy acceleration transmission makes chattering/rattling sound. The sound is very pronounced. Took the car to the dealer, they replaced the clutch, rear diff fluid, output shaft seal and several bearings in the trans with no lessening of the effect. Dealer stated no repair was possible. Trans still leaks from the output shaft seal, and still makes a nasty rattle under acceleration loads. Post repair, it is difficult to shift into 2nd gear when before the trans has warmed up. After a bit of warm up, the hard shift goes away, the rattle never does.