I have seen a few cases like yours and under the conditions you describe.

We use to see it a lot on Chevy small blocks. High rpm would pump a lot of oil up into the valve cover, overloading the valve guide seals. You would get a ton of smoke out the exhaust when you let off the accelerator due to high vacuum conditions.

This conditions is further compounded when there is sludge buildup on top of the head at the oil drainback channels leading to the crankcase. This slows the return of oil to the crankcase and it pools around the valves.

So it sounds like valve guide seals or cleaning return passages.

You only have just over 100,000 on the engine so I doubt you have piston ring wear. Besides you would seal oil smoke on hard accel too.

As an aside you might want to check and make sure the flame trap isnt blocked. It will contribute to oil smoke.