The vents in the valve covers serve 2 purposes in my estimation.
1) Allow intake of air caused by the vacuum caused by the road draft tube while under way. (Archaic crankcase ventilation.)
2) Allow water vapor to escape when not under way. Under normal conditions of a well broken in, but fully functional engine, you will see what appears to be steam wafting out of the vents. All engines, including modern engines produce this. You don't get to see this on modern engines since they have closed PCV systems.
If all you are seeing is some steam wafting out of the vents at idle or upon shutdown, you should be just fine.
Carl
