Oil burn cloud on engine deceleration

The smoke on downhill deceleration is a classic symptom for intake side leaks so it is not really at all weird; the vacuum is highest with the throttle closed and engine braking going on and engine braking is the most sustained going downhill. Put a vacuum gauge on it and look at the vacuum under those conditions and I bet you will see well over 20 in of vacuum even with your cam. That will suck oil through any small opening into the intake tract: seals, guides, intake manifold leaks.