Oil for scanning lamp track

I noticed that you recommended oil for the scanning lamp track, but didn't say what kind. I rarely use my scanner, so it has had a hard time starting up lately. I cleaned the track by hand and there was a little black residue. I find that the more I use it, the better it works. Would you recommend WD-40 or sewing machine oil or silicone lubricant or graphite lubricant or what?