You'll know that your valve cover gasket needs replacing when oil starts to leak from the joint where the valve cover meets the cylinder head. And if there's evidence oil is escaping from the rocker compartment, then you can bet air and dust are getting in. If you have a new car and you've noticed a valve cover gasket leak, then you might have a more serious issue on your hands as they are supposed to last for quite a while. This will cause problems with your timing components; when the moving parts like rocker arms or valve springs trade lubricant for debris, they could stutter or seize causing a massive valve-train failure inside your cylinder head. This would be a dramatic and extreme side effect of a cracked valve cover gasket, but leaking oil out into the engine compartment is, at the least, very messy and is a sign of a potential future problem. It is best to get it replaced as soon as you can.
Valve cover gaskets are made either of different kinds of rubber, cork, or composite materials, and prevent oil from inside the rocker compartment from leaking out. They are molded to conform to the space between the valve cover and the cylinder head, and have holes for the valve cover bolts to pass through (http://www.ehow.com/facts_7924753_valve-cover-gaskets-made.html). It is hard to believe, but early engines didn't always have valve covers. A lot of times the engine was covered by the hood or bonnet, however the rockers were exposed underneath. That meant excessive amounts of oil was leaking out of the engine, requiring the driver to constantly add oil to re-lubricate. The addition of valve covers (rocker covers in the UK) and valve cover gaskets eliminated that problem quickly. Now the rocker arms, lifters, and springs could be continuously lubricated without threat of losing oil. A quality replacement valve cover gasket will be able to withstand high-temperature environments for long periods of time without breaking the seal, and should last for over a hundred thousand miles.
It is impossible to fix a valve cover gasket leak without installing a completely new gasket. The good news is that the parts tend to be on the inexpensive side, and installation is not complicated. On most engines, your valve covers are right at the top of the engine, and fastened to the cylinder head by a handful of bolts. There are many applications where the spark plugs are installed right in the center of the cover, so you will have to replace the spark plug tube seals too. But as long as you can access the valve cover bolts, you should be able to install a new valve cover gasket with no problem.
When it's time to buy a replacement valve cover gasket, always choose a quality part. At Car Parts Discount, you will find parts from original equipment and aftermarket brands from manufacturers that specialize in sealing components for domestic and import engines. Some of our aftermarket brands, such as Fel-Pro, offer gaskets that will exceed the OEM in both durability and longevity. If you have the opportunity, definitely buy a new valve cover gasket from them if you need it.