That link was exactly what my old 88 cherokee experienced. I needed to replace the tubes from the valve cover to the air cleaner also. They dried out and the rubber portions cracked. When replacing the PCV valve I could see the caked up deposits in the opening. I removed the valve cover and found the top of the valve cover was caked with dried sludge at both ends. After cleaning the cover, replacing the PCV and plastic tubing, I had no more problems with oil in the air filter.