Cleaning and lubrication are the essential prerequisites for a well-functioning lock.

Locks contain many small moving parts and over the long life of a classic vehicle how often have they been lubricated? (maybe never!).

These lubricants are widely available (most hardware stores) and their small cost will return great rewards:

1. Modern lubricants especially "PTFE" spray - sometimes marketed as "lock lube" is our favorite. Apply liberally. Best for most locks - you can use lots if the lock needs it. "Dry Silicone" is not the same but is safer on rubber and plastic, and still is a good lubricant.

2. Powdered graphite is not sticky and doesn't help dirt to stick inside the lock, but it is "old tech". Do not overuse graphite, it's a solid and accumulates in the lock - and it's dirty. Buy a small tube and insert a small number of puffs.

3. Oil should be used only in emergencies. Any dirt that gets in the lock will stick there.

4. Products such as WD40 for "loosening", "de-rusting", "starting wet motors" etc are more solvents than lubricants. Yes they can be good for getting lock internals unstuck and moving, but once dried out (maybe after a few days) you should apply a recommended lubricant.