As always a search can lead to a thread that answers my question.
I had planned to disassemble my vacuum wiper motor to clean it, and did so yesterday.
After cleaning it I couldn't remember what I had read that should be used for lubrication. Was it petroleum jelly, brake fluid, or mineral oil?
Of course a seach revealed Vaseline. Thanks.
Motor now works like a charm. Surprising how much gunk is in those things.