Dorman 594-220 Engine Harmonic Balancer Compatible with Select Models

OEM look except the hub in the middle is a second design and requires  Genuine GM 89017622 Crankshaft Oil Seal, Front  for my 2003 Trailblazer with 4.2 L engine. The differences in the two harmonic balancers is that this one has a seal at the end and a step on the hub. The first design is a straight hub without a seal on the end. If you have a step on your original harmonic balancer then there is no need for a new seal. Not a big deal just adds another part to replace but it is a probable good to replace the seal anyways while you have everything torn down.