Which maintenance approach is crucial for ensuring the longevity of a lathe head-stock?

Scheduled lubrication is the correct answer because it directly addresses the need for maintaining the internal mechanisms of a lathe head-stock. Lubrication minimizes friction between moving parts, reducing wear and tear, and helps prevent overheating. Properly lubricated components can operate more smoothly and efficiently, which can greatly enhance the machine's reliability and performance over time.

While frequent cleaning, daily inspections, and replacement of parts are important for overall machine maintenance, they do not specifically target the critical function of lubrication. Cleaning helps keep debris and contaminants at bay, and inspections can identify potential issues before they escalate. However, without a consistent lubrication schedule, even clean and inspected machines may succumb to mechanical failure due to insufficient lubrication. Thus, establishing a regular lubrication routine is essential for the longevity and optimal functioning of the lathe head-stock.