Gone are the days when you could just take or make any old gasket and expect it to work as long as you plaster enough sealer on it. All types of hi-tech materials are coming into use, as manufacturers try to reduce assembly problems in spite of the increased pressures inside a modern engine. The result is that gaskets have become very expensive, so they should be fitted correctly the first time. This is why most important gaskets come with fitting instructions, which usually boil down to whether they should be fitted dry or covered by some compound.

2. Failure to clean the surfaces properly. This is a common fault, especially if you're not working on your own car. In many cases it's even worthwhile to use fine emery cloth to clean the surfaces, provided the surface stays flat.

3. Not preparing the gasket properly. You must find out, before you fit the gasket, whether it needs a coating, can be fitted dry, or needs some treatment. For example, some cork gaskets have to be soaked in hot water, otherwise they simply break up when you tighten the fasteners.

4. Not making sure the gasket is correctly mated to the parts concerned. The gasket may be wrong, with some of the holes not lining up. This is especially
dangerous if the gasket is for another model, and is almost correct, except that it blocks some vital oil hole.

5. Over-tightening is very common when you're inexperienced. In the case of a cork gasket, you can sometimes see the material being squeezed outwards as the fastener is tightened.

6. Using the incorrect tightening sequence. It's good practice to tighten a number of bolts from the middle towards the outside of a group in three steps. Initially just
until you feel some resistance, then about half the final torque, and finally to the correct torque value.