Honestly, have a good look round. If you can see any evidence of coolant loss elsewhere just say to the dealer – look could you just take the car back please (And dont mention what you’ve seen).
Some progress, Managed to get the chap to agree to a full repair with me paying only £100 (I have had qoutes from other garages in the region of £400) and a promise of a free MOT when its due.
Make sure you see the old matrix. MARK the matrix with a silver pen etc innocuously so only you would spot it. He might be bloody feeding it another bottle of radweld otherwise.