GOOD points, Tom! Breather problems are certainly a possibility, or simply a worn bore/rings.
As we know, with a properly functioning breather and rings that seal well, the engine will operated with NEGATIVE pressure in the crankcase, making it tough for the oil to defy gravity and move UPWARD.
(Crankcase negative pressure/manometer test is covered in 4.2 and 4.3 of the manual... 5" to 10" water column.)
While it's certainly POSSIBLE the guides are at fault, oil migration past worn valve guides comes up #5 out of the list of 5 causes of oil burning in the official Kohler manual.
Start at the top of the list/most likely cause and work from there. (Occam's razor)