Hello Erick,
Most often the crankshaft is not removed as the replacement of the lower rear seal half will most often solve the problem. In this way the crankshaft, bearings, timing chain etc. are not disturbed. If you choose to do both halves you will need to remove the crankshaft, unhook the timing chain which will disturb the camshft timing, ignition timing and injection timing also. Replacement of the bearings is not normally needed unless the crankshaft also needs reconditioned.
Replacing just the lower rear seal half does require dropping the oil pan which will involve lifting the engine or dropping the front subframe. I would also change the front cranshaft seal. Carefully inspect the oil pan for any metal or debris which could be signs internal engine damage.
