Should you repair or replace a letterbox lock?

Worth servicing

Stiff but working, with no visible rust. Often just accumulated grit. A clean and a dry lubricant can buy years — and dry lubricant matters, because oil attracts exactly the dust that caused the problem.

Door catches or drags, but the lock itself turns freely. That is an alignment problem, not a lock problem. Replacing the lock will not fix it and a new lock will develop the same symptom.

A recently fitted lock behaving oddly. If it was installed in the last year or two, the likely cause is torque or cam indexing rather than a failed mechanism.

Replace it

Visible rust around the escutcheon or on the cam. What you can see is a fraction of what has happened inside. Corrosion is terminal for a mechanism this small.

The key needs jiggling, lifting or holding at an angle. The wafers are worn. It will fail completely, usually at the least convenient moment, and usually within weeks.

The barrel spins freely without operating the cam. Either the cam has sheared or the retaining nut has backed off entirely. Both mean the mailbox is currently unsecured.

The economics, plainly

A service call starts at S$25. A new lock fitted, tested and warranted starts at S$50. That S$25 difference is the entire decision.

If servicing has a genuine chance of giving you several more years, it is worth it and we will say so. If we are looking at a worn or corroded mechanism, spending S$25 to defer a S$50 job by a few months is simply a worse outcome — and we would rather tell you that than take the service fee twice.