Over time the original rubber cover seals degrade resulting in oil leakage. These PTFE gaskets fill the gap, allowing the rubber to seal correctly once again.
Alternatively, if the rubber seal has deteriorated away in places or missing altogether, these can still be used but will require the cam cover to be modified. i.e, the bolt hole bosses will require sanding / machining level with the external flange face.
Note: Depending on the quality of the existing rubber seal, the bolt hole lugs may not be required. These are easily removed with a sharp knife (see cut line on pic 2). Always fit with the bolt hole lugs attached first!