Of all the many ways that a motor car uses to keep its owner honest, leaks are surely the worst.

Owners of older vehicles in particular, will know that leaks are the bane of our lives. We are talking of fluid leaks here, not the other kind of leak, where water gets into the car when you are driving in the rain, leaving you with damp carpets or a puddle in the foot well.

It's a sobering thought that there are no less than nine different fluids under the bonnet of a car. They are:

l engine oil;

l transmission oil/ automatic transmission fluid (ATF);

l brake fluid;

l coolant;

l fuel;

l shock absorber oil;

l power steering fluid;

l air conditioner refrigerant;

l battery water.

A variety of seals and gaskets are used to confine each of these fluids to its own allotted spaces, tubes and hoses. With the passage of time seals lose their elasticity, and then they can no longer do their job properly. Gaskets also become hard and brittle, and in addition the mating surfaces between which they are clamped, sometimes warp slightly, creating gaps which the gasket was never designed to cope with. This is when a leak appears.

A leak will make itself known in various ways. Often a few dark spots on the floor of your garage or parking bay are the first sign. Petrol leaks will betray themselves by the smell, brake fluid leaks will show up in an abnormal drop in the level of the brake fluid reservoir, an a/c refrigerant leak will soon render the aircon inoperative.

The first thing to do when you become aware of a leak is to pinpoint its source, and this is sometimes very difficult. In the case where dark spots on the floor are the tell-tale sign, you can put out a piece of white cardboard over the area before you park your car, preferably immediately after a run while the oil is still hot.

Afterwards examine the spots on the cardboard closely, and mark the part of the undercarriage from which the fluid is dripping with a small sticker, though you have to remember that air movement will sweep fluid backwards along the floor pan while you drive. Use all your senses when examining the spots.

Engine and gearbox oil will be dark and oily, automatic transmission fluid tinged with red, diesel fuel thin enough to soak into the cardboard, antifreeze mixture tinged with green.

Gearbox oil and diesel fuel have distinctive smells. Brake fluid, which will be brownish and soaked into the cardboard, can also be recognised by its characteristic smell. To confirm your findings, put a drop of the suspect liquid on the cardboard, leave it for a while and see if it matches the spots.