Engine oil is NOT the issue. Do NOT use gear oil. Many, many OEs will use transmission fluid in their manuals, as the oil is already in use on the assembly line for automatics, and the thinner viscosity results in better EPA ratings. It doesn't mean that it is the best thing to use in the trans. Several other Chrysler manual gearboxes came with ATF in them, and owners found out very quickly that flushing out the ATF, and replacing with *good* synthetic engine oil resulted in better shifting and better life, especially when being pushed. This subject has been discussed many times, but FWIW, I use Mobil 1 High Mileage (the HM part is very important!) 5W-30. We have thousands of trouble-free miles on ours. One of our cars is sitting at 218K miles, and shifts like new. IIRC, spec is 5W20, which may be fine in colder climates. We live in the south, and that extra bit of viscosity is just fine. Before anyone squawks, I use the identical fluid in my SRT-4 transaxles, which use the same synchronizer materials (plus a Quaife ATB differential). Those came with ATF+4 from the factory. Chrysler engineers quickly let it be known to enthusiasts to switch to the Mobil 1 HM 5W30, and that entire community has never looked back. If a high end fluid is of interest, I have used Torco MTF in those same transaxles with great results, but have not tried it in the Crossfire, as it just isn't being pushed hard enough to justify it, IMHO. The big thing is under no circumstance should you use gear oil (ie 75W90, 80W90, 75W140, etc) in these transmissions.