Steve,

I'm not real sure what your question is. Some valvecovers had the two little slit vents in the top. If yours has these and someone covered them somehow, I'll bet it was to stop the smelly vapors from coming out and fouling the air in the cab.

If the engine is worn out, these little slits will puke forth oily vapor and smelly fumes. Maybe someone was trying to pass the engine off as one in better condition than it was and plugging the vents was part of the ruse.

Stuart