A PCV is always a good thing to have,will it fix your problem? Prob.not. I would try and fix this issue before I spent the $$$ on a synthetic oil.Its not going to solve any problems by making the switch.
Do you actually drive the car? You need to start it up and run it around(at least 5 miles) to burn out all of the moisture that builds up in the engine.
Usually after about 500 miles but since its been 4 months I would change. No special oil needed, I like Delo 400 or Rotella myself,and a good quality filter (like wix) and you need to drive that thing!