No. It is all metal-metal seals, no rubber anywhere. Does the "base" mean at the joint between the upper and lower halves? If "bubbling up" there, you would have to remove them to clean the interface. However, they would have been leaking for a long time. Blow out the liquid with air, or w/ paper towels, so it is perfectly dry. It could just be the Gunk is sitting in the crack and not a diesel leak at all. If it is a leak, more likely it is where the tube attaches at the top and is dribbling down the side and collecting in the groove. The tubes often get a crack on the ferrule, from vibration.