Like most guys, I've been shooting oil down the carb opening for years with no problems. Shooting some down the glowplug hole is a good idea as well, but I never bother with that, even when I could.

Some of it depends on what you use for after run oil. If you are using a petrolium based oil, it can attack the rubber o-rings, but there are lots of good oils out there that don't attack the rubber, or at least don't seem to. I've been using ATF for after run oil, and while I haven't actually tried soaking some O-rings in it to see if they get soft, I haven't had a problem yet.