One way to determine if your valve cover is bent is to remove the gasket and put the valve cover back on to the cylinder head. When the valve cover and cylinder head come into contact, the cover should sit flat. If it rocks, it is bent. A symptom of a bent or leaking valve cover is a pinching of the valve cover gasket. This means that the gasket is sealing one area and not sealing another area.
Some valve covers are hard to access, because they are covered with other engine parts.
Chronic valve cover leakage can sometimes be fixed by using two gaskets glued together instead of using just one. The valve lifter is the unit that makes contact with the valve stem and the camshaft and rides on the camshaft. It opens the valve when the cam lobes push it upwards. The engine oil comes into the lifter body under pressure. It passes through a little opening at the bottom of an inner piston to a cavity underneath the piston.