Why does nobody talk about the pencil trick for worn bench dogs?

Last weekend I was laying out a bunch of repeat cuts on my workbench and the bench dogs were so loose and worn they kept tilting sideways. Every clamp-up was a fight. I tried shimming with tape, wrapping them in rubber bands, nothing held. Then my neighbor who builds cabinets came over and showed me his trick. He just took a regular pencil and rubbed the lead all over the sides of the dog before dropping it in the hole. The graphite fills the gaps just enough to make it snug, but it still slides out when you tap it from below. I did that with three loose dogs and they all held rock solid through a full afternoon of routing. My question is, how long does that graphite actually last before you have to reapply? I put new dogs in last year and they were fine until now, but I dont want to re-pencil them every single project.