I need to pull a 35 year-old pipe out of the soil stack tee and replace it with a nice new one when I change the toilet, because the old one has been badly painted - you can get white ones now - and the toilet connections are all sealed with mastic or putty - nothing in this bathroom was installed properly by the housebuilders. There's also not much fall (ok, zero) between the pan outlet and the stack but the new chodbin has the same 180mm outlet height as the old one, so it should work as it did before.
Anyway, are the O-rings in these soil tees universal? I doubt the original is much cop. I did the same job in the last house but that pipe had only been in situ for 21 years.