When repacking a stuffing box fitted with a lantern ring, which of the following precautions should be observed?

Correct Answer: Option D — Replace all of the packing rings.

When repacking a stuffing box, all old packing must be removed to ensure uniform compression and prevent uneven wear on the shaft or sleeve. Mixing old and new packing creates voids and hot spots, which can lead to premature failure and excessive leakage of the sealing fluid.