I had some plastic shafts break too. Particularly when trying to remove the hard plastic mk1 knobs. If memory serves me the expected service life of the original Bourns encoders is 100,000 turns, which isn’t that high. They have metal contacts inside which get grooves worn into them from the metal wipers, and are prone to oxidise as well, causing errors. The wipers can also lose their spring pressure and stop making good contact. As for the push button, that’s just a simple bit of shaped metal with a pretty low chance of damage as it has limited travel within the encoder, so push away. I’d say they are worth replacing after 20 years if you’re up to the job but a spray of DeOxit D5 also keeps them going, if loosening up the feel somewhat. A new set of encoders does feel pretty lush.
I’ll post pics of some destroyed encoders if I can remember where I put them. Have a whole bag full from doing my mk1 MD & MM.
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