In my experience the gaskets tend to leak, but that's just what's happened on my GN in the past. Last time I had mine apart I smeared some black RTV on the surfaces and no leaks since. Also used loctite on the bolts.
The GM part# is 24502089. In October there was a GM dealer in Pueblo, CO with qty = 4 in "old" stock that the parts guy wanted to unload for cheap ($4/ea). 719-544-4423
Could you hook me up with 2 new gaskets? I can send payment via paypal or by US mail. Please send me a PM with your paypal address or your mailing address.