Unless the coil is still running very hot, getting visibly distressed AND the car is not performing properly (eg. mis-fire, poor fuel economy, difficult starting, etc.), I would be reluctant to worry about it. I find that I can usually spend enough money replacing parts that definitely need to be replaced without worrying about any that maybe don't look quite right. I guess you need to look at what can happen if you don't replace it. I am in favour of replacing something that will cause damage or is dangerous if not replaced but all that can happen with your coil is that the car will stop.

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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.