A nasty gash

Discovered a hole in the radiator tonight. This may be a clue why the radiator will only take half the volume it should. This hole is spongy to the touch. Methinks someone has poured in Radweld in quantity until it stopped leaking. A new radiator is no longer available but at last price of £483 I don't want one ! Tatty one on e bay for £50 but would rather get it fully repaired than risk that one.
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