Low engine oil: If engine oil is low, it can lead to friction inside the engine, causing the engine temperature to rise, eventually leading to failure and even fires.
Burning smell: Cracked and worn valve cover gaskets accumulate compressed oil underneath which can then drip into other high-temperature areas of the engine, such as fuel intake or cylinder heads, leading to a burning smell.
Rough-running engine: oil leaks from the gasket are so bad that they can drip down onto the spark plug galley and inside the plugs themselves causing misfires and engine performance issues.