gbhrps,Thanks again for your reply. I think I know what had happened. Before I parked my car on the inclined driveway, I filled the gas tank. It had a full tank. When the car was parked inlined drive way, the gas overflew and dripped on the canister. When I later parked on the street, the overflown fuel 'cleaned' the canister and left a stain on the street. It stopped when the overflown gas was gone. It never leaked since. I think the mistery is solved. Not sure if this had caused any damage to the canister. Thanks again.