35 years ago, when I first bought my 72, I too was concerned about the small amount of oil in the primary. When I filled the primary with the proscribed amount of oil (the shop Manual is wrong) it would soon be sucked into the crank case and pumped back to the oil tank which then over flowed. I'd take the cover off and there was very little oil left. Drove me nuts for months. Finally talked to my parts guy and he said not worry. There is mist of oil that comes through the unsealed main bearing and that's what kept the chain lubed. To prove it to myself I again took the cover off and hung a piece of cardboard about an inch away from all the moving parts. Fired the bike up and sure enough with in less than minute the cardboard was dripping oil. Put it all back together and have not thought about it since.