1992 Nissan Maxima GXE SOHC Crankshaft Pulley is Wobbling?

Now, correct me if I am wrong, but doesn't the Crankshaft Pulley sit on a sleeve? Would the sleeve be bad, & therefore allowing the Crankshaft Pulley to wobble? Also, the rubber "membrane" or Harmonic Balancer rubber piece leaked oil, black oil, bot like my engine oil, it has stopped. Would I need to replace the sleeve & the rubber piece then? I am unsure what to do. I know that the wobble is my biggest concern, but since I will be in there, would I be able to find just the rubber part of the balancer, or do I have to buy a whole new embly?