Les
Is it correct that the car was not serviced for 3-4 years, and what was the pattern of use in that time?
The problem with extended periods of disuse is that the corrosion inhibitors in the antifreeze become depleted as they stop corrosion. If the fluid in the radiator matrix isn't circulated (engine not started/up to temperature, thermostatic valve not open) then this local radiator fluid may become different in composition to the rest of the system (which will still test as within concentration limits). Galvanic corrosion within the radiator matrix/welds can then cause perforations (evidenced by rusty water from an aluminium radiator).
I write this with some sense of guilt, as I have a number of cars which suffer issues because I simply don't have an opportunity to use them sufficiently.
If Morgan really are offering to cover half of the repair cost, personally I would grab this opportunity with both hands.
