The correct answer is A) seal failure usually requires the immediate removal of the pump from service. The reasoning behind this is that mechanical shaft seals are designed to provide a tight seal between the rotating shaft and the stationary pump housing. Unlike mechanical packing, which can often be tightened or adjusted to address minor leaks, a mechanical seal failure typically requires the immediate removal of the pump from service for seal replacement. This is because a mechanical seal failure can lead to significant leakage that cannot be easily remedied without replacing the seal. The other options are incorrect because: B) mechanical seals can be designed for high-pressure applications, C) mechanical seals do require periodic maintenance and adjustment, and D) mechanical seals can be designed for high-temperature applications as well.