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What you are describing sounds like blow-by.
As the engine wears the compression rings loosen and allow combustion gasses to blow-by the compression rings and down into the crankcase. The gases then make their way up to the top of the valve cover through the oil passages and then vent out the PVC or breather system. These gases are hot and will burn some oil on the way up and out, thereby creating the smoke you are seeing.
The only real solution is to rebuild or replace the engine.
You could confirm this with a compression test, but really, the only way to get gasses in the crankcase is from blow-by.