In this pic:
See the small cover over the wires on the nosedrive end of the SC? Pull it off. Look right behind the tensioner assembly on the nosedrive itself. Between the nosedrive and alternator, but on the nosedrive (back side). Look straight down. You'll see the plug. Black plug with a hex socket in it.
the procedure is in Techinfo. A pump sprayer (windex) or syringe with a tube in it should be used to suck it out. Fill it back up to the bottom of the plug threads. Use ONLY GM SUPERCHARGER OIL, or INTENSE or ZZP (same stuff).