Just an update... The crush washer is 1/2 inch in size, and made out of metal. They should have a selection of crush washers at your local auto parts store. I don't have a GM parts number, but as long as you know 1/2 inch and metal (might be brass? I'm not sure) you should be alright. I picked up a 3 pack from autozone for around $4.

And yes, the deal from advance auto parts is pretty good- 5qts of synthetic + a synthetic brand filter for $29.99. I'm currently trying out the 0w-30 oil (mobil 1 advanced fuel economy) to see if it actually makes a difference. Yeah, I'm probably throwing my money away, but I'll let you guys know the results when i'm all done.