Having trouble with a 66 230 SL after rebuilding the engine. Starts and runs on all six till it warms up, then starts dropping out # 6 cylinder at idle. When rev ed up that cylinder hits up and doesn't mis on the road. Checked over everything with leak down and readjusting valves. Finally tried swapping the lines off the injection pump between 5 and 6 and the mis moved to cylinder 5. I also swapped injectors around without helping the mis. Seems to me that the pump needs rebuilt. Is There anything else at the pump I can try before sending the pump out?