Right, the rain stopped and I had another look and noticed that burning off the glue revealed a small hole in the crimped flat. I cleaned it out with a few small slow-running drills until it touched the cable and increased drill sized until it matched that of the hole. Now looking into the hole with a torch, it looked shiny silver not copperery colour, so maybe the solder had wicked down. I checked for other holes and there was one 180˚ opposite so did the same with that, it looked silver inside too. I couldn't resist it, but set up everything again and pushed some solder into these holes too for good measure and then I have reconnected, left to cool. started the car, starts fine, and didn't get warm. I could do more testing but weather is terrible and don't want to overthink the whole things so will reassemble between showers and see how it goes longer term.
One of those dremels with a sanding tool would be useful as I am trying to scrape it with a stanley knife.
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