I'd say if it's not leaking enough to cause a drip, it's better defined as "seepage". He may be trying to help you by warning you early. I'd wait until it started actually dripping. If the thought of this horrifys you in some manner, then have it repaired.
I believe there is either a gasket or O-ring between the sensor and the oil pan, available seperately. I wouldn't authorize the replacement of the sensor if it's leaking between the sensor and pan.