The whistle motors on my 6466W tenders have a channel on top of the whistle motor brush plate that is approx 1/8" x 1/8" x 1" long. The top of the armature shaft extends through the brush plate into the channel. The channel is not electrically connected to anything. Loco motors do not have the channel. What is the purpose of the channel?
Too much oil is just as bad, if not worse than too little. You might want to moisten the wick with a little oil. It will only work if the wick is rubbing against the rotating shaft.
I generally do not use oil on the brushplate side, unless there is a bronze bushing or bearing. I put a light coat of Labelle 106 grease on both the shaft, and the inside of the hole in which the shaft turns.
As far as oil wicks goes… many Lionel diesel motors have oil wicks mounted on the brushplate… Scout motors typically have an oil wick as well.