That being the part # for the piece the o-ring is attached to, not gonna do you a lot of good. The seal is not a separately serviced part by GM.
My recommendation would be hit a real auto supply, not a box store, and look at their o-ring selection. Take the adapter with you, obviously. Real parts stores are getting scarce but a NAPA may have misc. o-rings in stock. In the past I would recommend Carquest as well but since Advance bought 'em out, I dunno. Could still be worth a try.
You may need to glue the o-ring in place if you can't find the exact same shape. The original looks like a square-edged o-ring with a cut in the middle, similar to a thermostat seal from the same era.
Richard
