I was sweeping when the broom head and handle of a Libman broom broke apart. Upon trying to reattach both parts together, some black, viscous liquid between the broom handle and head got on my skin and stained it momentarily. Should I be concerned?
Sounds like water that got in. Water seeps between the handle and broom head and also will seep into the handle where it can remain for weeks. Same will happen if you leave it outside in the rain with the handle upwards.
Unless it was submerged in toxic waste you should be fine. Wash your hands with warm water and soap. I had a broom of that sort left forgotten for weeks soaking in a bucket of water.