As someone does that does his own maintenance, one of the jobs that I dread most, but I know has great value, is changing the fluids in transmissions and differentials. In manual transmissions (Is there any other kind?), transfer cases, and differentials, the fluid is unfiltered, subject to a lot of heat and shear action, and in many modern cars the fluid volume is being reduced to save weight and space. Yes, I know many manufacturers say these fluids are "lifetime". Well, when they...