My o-ring doesn't attach to the filter itself, per-se. The filter does have a flat rubber ring already stuck onto it, but the actual o-ring goes in a separate groove around the filter socket. Hence having to be careful when changing it that absolutely NO grit is anywhere near it, no matter how hard it is to see.
Otherwise, you get a gap, the hot oil melts the seal and your engine lubing fluid pisses out halfway down the motorway, resulting in a fucked engine all because a 2p bit of rubber was slightly gritty.