I've done several oil changes on the 2.2L Ecotec on my mom's car and I've not replaced the o-ring on the filter cap yet. I expect the one on the Saab to hold up just as well, it's the same part.
As far as the oil drain plug gasket, isn't it an attached rubber gasket? That's what the 2.2L Ecotec engine has on it's drain plug, and I've gotten upwards of 100,000 miles worth of oil changes out of this type of drain plug, my old car, a Ford Contour, had this type of drain plug w/ attached rubber gasket.
If not then I may just have to go to a Chevy (or Ford) dealership and get a new drain plug for my Saab

(the thread size is identical between the 2.0L Ecotoec, 2.2L Ecotec, and the 2.5L Duratec that's in the Contour I had).
On the other hand maybe I should get a Fumoto valve and make oil changes really easy...