I've run K&N in about 5 different vehicles and have never experienced a problem. This includes cleaning and reoiling the filters. No problems.
If someone got oil on a MAF from the K&N, then they must have tried to clean the filter and reoil. I would ask if they oiled it with something other than the K&N oil for air filters or if they used an excessive amount.
The instructions for doing it are to clean and let it dry totally, then spray lightly so the whole filter turns the redish color of the oil.
As well...you might want to check if they removed a MAF screen, that would affect the idling if a screen is there to straighten the air out like our bonne'* have.
00 Regal GS: All kinds of cool stuff.