I'd take the clutch apart again. Remove the entire unit, springs / pressure plate / friction plates / boss nut / tab washer / then the boss / spacer washer / then the clutch basket.

Check the condition of the splined shaft.

Then put just the boss on the splined shaft without the basket behind it and see if it freely slides up and down the shaft to check for interference or damage between the inner splines of the boss and the shaft splines.

Then check the basket will slide nicely on the shaft, back to where it should sit, by itself and again check for interference / damage between the mating parts. There should be no seizing or need for heating components. In theory these components are not tolerance fitments.

a thing that catches a lot of us out is the alignment of the pull rod teeth and the pull rod shaft regardless of the dots lining up. It has been known for this to go wrong and the pull rod shaft ending up with damaged teeth.

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I have a lot of growing up to do. I realized that the other day inside my fort.