I'd do a compression test first-check balance between cylinders.Look for something obvious. Then a leakdown.
O-ring seals SUCK. Machine for teflon seals or at least get the good rubber sleeve seals(they stay put and last longer) Depends on the valve springs you have though(Internal diameter) If it's only smoking when you stop then check the needle and seat or spray carb cleaner around the intake gaskets. You have higher vacuum at idle a may suck oil from a warped intake .
Although a MO doesn't have much vacuum anyways. But it sounds good doin it!!
Good luck