To me it's a new leak, but then I've only had the car since last August, and with the winter months and now lockdown I haven't covered many miles in the car. I have done some reading up and it seems a dodgy plug weld is not uncommon. I'm leaning towards a thorough clean up, delicate grinding of the weld and surrounding casting and applying two coats of JB weld. If that doesn't do the job then it will be off to a welding specialist who can weld the steel weld to the cast casing.
