If the modulator is original, it's a safe bet that it could stand to be renewed. A simple job, complicated somewhat by access issues with the transmission in the car. If you decide to replace the modulator, I would suggest procuring a new pin (approx $3) at the same time, as it is very easy to break the original one when the old modulator is removed. (This assumes that you have the version with the plastic pin.)

Then, of course, you have to adjust the new modulator. And the procudure for that is subject to substantial debate. I went to the trouble of fabricating a gauge and setting the recommended pressure. The transmission shifted poorly at that pressure, so I adjusted by feel from that point.