If you mean the sparkplug tubes are leaking oil inside the tubes this can cause a misfire if the oil gets past the coil boot seal to the sparkplug also K&N air filters can have excessive oil on them which often fouls the mass air sensor (MAF) so be sure the mechanic knows the K&N is in the car & the MAF may need to be cleaned. If these are the cause of the problem it won't cost much so wait for the estimate & post here for further advise.
