Was your oil pump overhauled or checked when you did the rest of the engine?

It sounds like to me the oil is draining out of the oil pump when you shut down and it has to re-prime itself on each startup. If only shutdown for a while the oil hasn't had a chance to fully drain. I'm not that familar with the C223's oil pump and oil gallerys to suggest anything specific.... Now if it was a TD-18 I could help, I've just done one, big and clunky, the oil pump stands about 2 feet high!