I am paying careful attention to the behaviour of the clutch and shift action at the moment (I need to as it really is not very easy to drive with this problem). Shifts (between any gear) below 2000 RPM are fine. From 2000 to 3000 RPM they are difficult. Above 3000 RPM, don't even bother trying! One thing I must comment on though, is that from a standstill the clutch is the smoothest it has been since I have owned the car. No shudder at all.

I also spent some time studying the WIS in the hope it offer some clues. I captured the most useful information in the attached screen shot.

Attached Thumbnails

 

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.