The component most likely to fail with a boat in the air, and the one with the least honest warning.
Wire rope wears internally first, at the points where strands cross and move against each other under load. By the time a broken wire appears on the outside, the internal cross-section has been reducing for a long time. Visible damage is a late-stage symptom, not an early warning.
Cables on a lift have done the same cycles under the same load in the same water. If one has reached the end of its life, its partners are close behind. Replacing one leaves the others carrying an increased share against an unknown remaining strength.
A seized or grooved sheave will destroy a new cable quickly, because the cable is being dragged over a fixed surface rather than rolling across a turning one. Replacing cable without checking every sheave is the most common way to buy the same repair twice.
On an interval rather than on appearance, because the wear that matters is internal. Marine environment, cycle frequency and load all shorten it.
Yes. They have the same service history. The one that looks fine is carrying the same hours as the one that does not.