PCV Milkshake-Rusty oil dip stick

[SoCalSlaughter]

Truck is a 90 Suburban 5.7. About a month ago I went to check the oil, and noticed the top of the oil dip stick (Closest to handle) had rust on it. Oil is clean and full. Removed oil fill cap and its clean. Removed the air cleaner assembly and noticed where the fresh air tube comes in from the valve cover had a milk shake residue on it, also alittle bit on the throttle body itself. Coolant is full and green. Truck doesn't over heat. Replaced intake manifold gaskets to see if that would fix the problem. But after a few weeks the oil dip will get rusty again and the milk shake residue will slowly come back through the fresh air tube from the valve cover into the back of the TBI. Note, I dont make short trips in the truck. Work is about 15 minutes away, mostly freeway. Anything I should check for? Thanks in advance.