I think I once actually saw this. When I first started at the local telephone company back in the day I was shown the corporate PBX system which was interesting

I think I once actually saw this. When I first started at the local telephone company back in the day I was shown the corporate PBX system which was interesting because it was a small step by step system in an era where such things were considered obsolete. There was a rubber belt running on pulleys in a transparent box. There were several magnetic recording/playback heads in contact with the belt. The bottom of the belt passed through a pool of lubricant. It picked up so much that the heads left a wake and had a kind of a bow wave. lubrication was apparently very important.