Intermittent Speedometer Reading
 

The speedometer (92 500SL Analog Wired) is functioning as though it is stuck sometimes. At times, when auto is first driven, it does not move. Then, after driven a few miles, it suddenly begins to function (unsure of accuracy). Can this be a problem of inadequate lubrication and if so, how do you lubricate it? Also, can the analog speedometer/odometer be replaced with the digital type from same model later year? Appreciate any help with problem.