I recently obtained a used Ngraver hand engraving tool that runs on a rotary
shaft. I cleaned some "gunk" out of it and it runs well, but what is the
proper lubrication for it? Graphite? Light oil? Nothing?

I had an Ngraver tool once, and IIRC the proper lubrication was Lubriplate or
some other light grease. Hope this helps.

Jim
Don't raise the bridge, lower the water.