It goes in until it bottoms out and doesn't go in any further. Sorry I can't be more technical than that.
Are you using the correct driver tool? If your not you might have cocked it.
YES no seal is a bad idea, pull it all back out. You'll probably need a new Gimble Bearing though. The genuine Volvo parts come with an installation booklet that also tells you the tool numbers (ie special tools needed). The booklet kinda reads like stereo instruction but you'll be able to get a better idea of what your doing by reading it. hope this helps and good luck!