Replacing the PCV is another good idea.
If you're losing oil, you'll need to find out where it's going and at what rate. Just keep an eye on the level for a while. If a valve cover gasket is leaking substantially, replace them both.
It may just be the odor of used oil that you're noticing, but run it a while and just keep an eye on the level. Find out how many miles it takes you to be down a quart and report back. The UOA will tell you if there's fuel in it once the time comes. Don't worry about a heavier oil just yet; some time will be required to find out what's going on.