I used a 6B graphite stick on my track a few years ago and have never had to clean it since, maybe just needing the odd touch up with the stick in places.
The only odd thing I have and haven't thoroughly investigated it as it doesn't seem to have any ill effect, is that I noticed I have a high resistance reading across the rails.
With no stock on the track I get a reading between the rails of 13kΩ. The layout is wired in two sections so I split the bus and get 35kΩ on the terminus and 20kΩ on the depot.
I have put this down to graphite bridging insulated joiners around the frogs but as I said, whatever the cause, it is having no ill effect on the running performance.
I was wondering if other users of graphite get this.