If it is definite oil stains then it will be the top oil seal in the gearbox worn out allowing oil to come up the agitator shaft into the water. However, if it is just small black spots then it may be a buildup of soap scum on the inner & outer bowl which goes black & comes away at times to mark the clothes. If you suspect that may be the case rather than actual oil, try doing a full load hot wash with no clothes in the bowl & put in some descaler which can also be used in dishwashers to loosen & remove the dirt buildup.
Lincoln Appliance NZ, January 2009
