Syncro 4&4 Discussion and Q&A last answered over 2 years ago.
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get the 27mm nut end of a scrap cable and screw that on you can lever against it and when fully tight should in conjunction with your penetrating oil allow you to turn it and crack the corrosion, as once the rollpin is punched out of the case the sleeve can rotate in the wall of the case
be aware the alloy the sleeve is made of has that poor combination of soft and brittle, easily deformed yet the shaft runs in close tolerance precision bore with in it and is good quality
I made a tool using the end of a cable to fit to the slide hammer but eventually that wasn't upto the job so my machine shop made me a proper tool adapter for the slide hammer which does the job effortlessly in the workshop - insitu is a bit tight for that sort of solution though