Cooler hoses going through the wrong holes
Undoing the cooler hose fitting: Spanners on both the cooler hex and the hose fitting hex, in such a way that squeezing the two spanners towards each other applies all the force to the hose fitting in the 'undo' direction, and little if any to the cooler port itself.
Reputable supplier and standards info, something you wouldn't know with braided.
Despite claims to the contrary there is no way these hoses could be pushed through the grommets if the grommets had been pre-fitted to the radiator diaphragm panel. Even split they are very difficult to fit and remove with the hose already in the panel, although the new hoses being smaller make it slightly easier.
Cooler hose routed above the gauge hose, giving better access to the distributor cap ...
... albeit closer to the filter than before.
Plenty of clearance to the inner wing though, lack of which caused the problem with the original filter adapter, and had dented the panel (circled) on a bend, which is a lot stronger than a flat panel.
Bead of oil from the source of the leak ...
... which when wiped away is indistinguishable from the very fine crazing over the general area.
Internally looks ok ...
.. until slit lengthwise and opened out, then a lot of fine cracking (the long cut is from the blade I used to slit it) - worse then the external crazing.
Markings on the long hose (not the failure), indicating it had perhaps already been replaced. No markings on the failed hose, perhaps original.