Dear Mike and Dave,
My speedo gear and 90 degree speedo drive unit mutually took each other out recently after twenty years of peace. In the course of replacing them, I had occasion to speak to Lloyd Butfoy and I asked him about how to lube and maintain the 90 degree speed drive. His advice was to remove it from the ZF yearly and lubricate with WD40 or similar lubricant and add a dollop of graphite lube to the speedo cable. Yearly! FWIW. I don't know any better than what I am told.
Warmest regards, Chuck Engles