Looking to change the fluid out of my manuel transmission on my 95 9000 cs converted to cse FPT!! Car has about 204xxx miles. Shifts good and smooth no crunches. But I have no idea when it has been changed. I see a little drip coming from the transmission, nothing major. This is more or less preventive maintenance. I have been searching what fluid is the best some say synthetic some say dino oil which is what it calls for. Also I am in a climate that can get as hot as 95-100 degrees F and as low as -10 degrees F. I have been looking around and good stories have been coming from Amsoil 20w-50. I called a 2 dealers. One said they use synthetic 10-30 and other said they use 75-90. Based on my situation with the car is self and the climate what do you think is the best oil that will be excellent in my climate and keep my trans in good shape.