I wanted to understand when the Limitation Act time limit of 6 years expires. Is it calculated starting on date of car purchase by 1st owner? Or is it from the date of the last faulty warranty / dealer repair?
This is what AI says:
"For a warranty repair, the 6-year limitation period begins on the date the breach of contract occurred—which is typically when the faulty repair was originally performed, not when the car is supplied, nor when the latent defect eventually manifests or causes failure."
I.e. the date you received your last faulty rad replacement, not from date of purchase, nor when the radiator failure occurs.
However, AI is notoriously unreliable and no case law or statute reference is cited. This position seems sensible, to prevent car makers stringing customers along by making unsatisfactory repairs throughout the Limitation Act period, then walking away. But 'sensible' doesn't mean 'true'. For example, on the other hand, is it fair on manufacturers that a repaired radiator should always be expected to last a further 6 years?
I'm lucky so far and not in your position, but if I were, I think I would get advice from a solicitor (or at least the citizens advice bureau). if I had been through what you have been through, and was coming up to the 6th anniversary of the car's first registration, I think I'd want to know my status and whether my position would be helped by putting anything in writing to MMC / supplying dealer.