Sniglfritz, twasn't me that said you couldn't re-ring in car.
However, having recently had the head off and the oil pan off as well, I agree with Rocketman that it is almost certainly just as hard to pull the head as it is to yank the whole engine. If I had it to do all over again, I would have pulled the engine. There seems to be an equal number of pain points and having it out relieves a few (timing belt and water pump pulley pain). Pulling also allows a good clutch inspection and replacement parts there are dirt cheap.
Greyjake, it is really hard to know what you are dealing with unless you can eliminate issues one at a time. I urge you to get the engine hot, shut her down, prop the throttle wide open, pull the plugs and check your compression on each cylinder counting revs. Do about 10 each. Write them down. If #4 is that bad, it should show up. If the compression isn't bad across the 4 cylinders (check shop manual for ranges), proceed with the following.
That turbo oil seal is very hard to work around. It makes it hard to know just where other problems are for certain. I'd take the intercooler off, dump the quart of oil that is most likely in it out, and degrease, wash it out and get it dry before reinstall. Replace the turbo CHRA, then with everything apart, clean out all the oil from all the intake piping. Check your PCV valve, it should rattle freely. Consider replacing it as well. If you have the valve cover off, check the seal on the baffles, I'd just count on redoing them with the right RTV and solvent first to assure a clean bite and a proper seal. Button it all back up, eliminating the "S" hose from the valve cover vent and put a cheap-o breather filter on the valve cover. That will allow you to see if you are still oiling somewhere.
Start with the compression test, that will define your next steps. I've been there recently.