A seal in service stays wet and gets lubrication and is less likely to fail. A seal that is not in service drys out and is more likely to fail. Common for very low mileage older cars that were stored and put back into service to have all the seals leak when the car is put back into service. 20 year old rubber will dry out just sitting. The seal is easy to change and you will want to change all 3 seals.