As you rightly point out, a combination of glazing, some wear and possible hyraulic problems could all cumulate to cause clutch slip before the wear limit is reached. The issue with the hydraulic hose was in the back of my mind when I considered the possible cause of my problem. I am aware of constricted brake hoses preventing brakes fully releasing and as you point out, a similar condition with the clutch hydraulics could prevent the slave cylinder fully returning leading to slip. Thanks for the suggestion. I will investigate that as a possible cause of the problem.
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.