Papa Nick,
I was thinking today (a dangerous thing to do, I know) while driving my Model A home from a club function about the speedometer in my car. It just turned 85,000 miles. I was wondering if I should oil it. I believe that is the accurate mileage for the car, and speedo.
My method would be to take the cover off and apply drops of 3-In-One oil to all the moving parts, avoiding the hair spring. I know there are people out there who would be uncomfortable doing this but still need the maintenance of their speedometer. (Do they need oil ever so often?) My advice for them would be to send the instrument to you for maintenance.