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Hi Piet,
in fact the strokes are tyical for a quick stress (temperature\water stress). After a raining season high temperature and low rain can increase the risk for strokes.
I saw other pictures and the spongy tissue you have inside the old crown head is Esca’s clear symptom.
Advice: According with your pictures, if you want to start the branching, try to select some shoots in spring under the crown head and cut the spur there. It is much better if you start the branching in that point, so you can take the direct sap flow before this point (full of died wood).