It's really more than one o-ring, there's 3 for your car when the pan is removed and yes, I've done it. There's one for the sump and two that go between the pump and oil filter housing. The pan itself isn't hard but getting there is yet another story for a guy in his own garage with minimal tools (assuming here?). The engine must be supported, the engine mounts unbolted from the subframe, the steering rack unbolted from the subframe with sway bar link ends, then the subframe must be lowered so that the pan clears the sump. There is no gasket, it's a chemical gasket which I like to have it sit overnight before adding oil even though they say it's not required.