The road draft system uses the road draft tube to vent the crankcase. Air to replace what is "drafted" out the tube comes in through those slots on the rocker cover. A primitive setup. But that is how the road draft is supposed to work.
There are many different versions of the road draft tube. But remember that they are all intended to exhaust the crankcase fumes, except for the pcv equiped gmc's and some 235/261 Chevy's.
