Cruise control surge

[Duke2.6]

'88 190E 2.6, five speed manual tranmission, 72K miles

The cruise control surge is intermittent and seems to correlate directly to an intermittent speedometer needle flutter. I recall from looking at the cable some years ago that it appears to be sealed with O-rings at each end, so the normal cleaning and relubrication that will usually solve speedo flutter on my older GM cars doesn't appear to be an option.

Both my speedo head and speedo cable were replaced under warranty, but they was about 10 years ago, so I figure the needle flutter, which is the likely cause of the cruise control surge is probably just an age phenomenon.

Has anyone else experienced this problem? Does anyone know if the cable can be lubricated, or is the fix to install a new cable.

Duke