I have had success with penetrating oil and the sharp end of a scribe. I ta p out the cable from the back side. I use stainless steel cables on all my vintage bikes, even though it is not period correct. Sram makes a nice s.s 1.1 gauge cable designed for grip shift that works great for those smaller diameter heads. One can also file or sand the head to reduce the diameter s lightly so it fits the shifter better.
Sacramento, California USA
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