The function of an O-ring as a seal is mainly to hinder unwanted movement of fluid between two or more regions. In the case of your BMW 323i, it prevents oil from leaking out of the vehicle's filter. The basic components that make up the seal are the O-ring itself and the contact surface. When you are experiencing problems from either component, the most apparent warning sign is a big puddle of oil under the car. Here's a list of common culprits that will bring your o-ring to premature wear:
High-pressure systems like the oil filter on a vehicle often bite or nibble the downstream side of the O-ring. Various reasons can be blamed for this: it may be that the O-ring material does not meet the standard grade requirement for the BMW 323i or that the O-ring suffers from machining defects, leaving the O-ring gland with sharp edges. It can also be that the O-ring size is too large for the gland, that it takes its toll from friction every time it expands and compresses.
It is easy to spot whether or not an O-ring suffers from abrasion. Does it possess a flattened surface on one side of the O-ring's cross section? If so, then the O-ring definitely suffers from poor lubrication. The metal surfaces may appear smooth, but its fine structure can still act as an abrasive during excessive temperatures. The only way to solve this is to properly lubricate the component before further damage is incurred.
Like in all things mechanical, improper installation is the bane of O-ring components. Notice any short cuts or notches? Maybe the surface is somewhat skinned or peeled? However mild the damage may seem, it will hinder the O-ring from functioning at optimum quality. To solve this problem, you will need to purchase a new O-ring and make sure that you properly install them this time. Be wary of the sharp threads you need to pass the O-ring during assembly. Also, avoid twisting or pinching the O-ring during installation.