I just bought this car used and thinking about changing the fluid. When I move the shifter, from reverse to drive, park to drive, etc., the transmission clunks and shifts very hard. I noticed the car doesnt do this when it's cold in the morning. Other than that, the tranny shifts firmly and does not slip. Anybody familiar with this symptom? If the tranny's on its way out, I wont even bother with service. Please help.