[TR] Erratic Speedometer

[Hdefer]

My TR3 speedometer  whips at low speed, steadies out mid range and  
then becomes erratic around 60 mph. I replaced the cable, routed it  
exactly same way as the original , but the problem remained. I  
suspect it is still a cable problem.
I read somewhere that lubricating with oil or other liquid is bad as  
the factory carbon lubricant may migrate with it upwards into the  
speedometer bearings which is harmful in the long run.
Is the speedometer the more likely culprit? Has anyone serviced one?  
Could lack of damping with age be a problem?

Hans, 61TR3A