oil leak on 2001 Ford Focus

The car has oil leak,a little, on june it was fixed, the mechanic put a new oil filter, a Timing Belt Componet Kit, oil pan Gasket set, and W/pump housing gasket w/pum outlet seal, the labor I think was too high, and again has a leak, what could be, please,

Asked by for the 2001 Ford Focus
Valve cover gaskets are common failure on these engines.