It is the New Venture Gear (NVG) T-350 transaxle. Have you tried a fluid change with the recommended fluid before condemning the gearbox? MTX00.jpg
A GL-4 spec fluid has additives for the brass (yellow metal) synchros if you are getting a 'crunch' when shifting. http://www.mobiloil.com/USA-English/MotorOil/Car_Care/AskMobil/GL-5_and_GL-4_Gear_Oil.aspx
Finding a good used manual transaxle may not be easy. I believe that the Neon, Sebring, Stratus, Breeze and PT's all used this transaxle. I'm not sure if it has to be a 2.4L only or not.