I agree with Todd, it sounds like the balancer has a problem, while he has it off check to see if there is a groove worn around the balancer where the seal sits, if so they sell a repair kit that has a thin stainless sleeve that presses over the balancer to repair it. If you have calibers check the wall thickness around the balancer to make sure it's concentric with the crank shaft hole and the dampner hub.
JMO
Zip.