I've posted this to Kimboo also, but FYI the "reasonable time limit" is specified within the Sale of Goods Act. Section 48 stipulates that where a fault that could not have been identified by reasonable inspection presents itself within six months of purchase, then it can be assumed to have been present at the time of purchase. The law is clear on this guys, if you have been supplied with faulty / unsuitable goods then you are lawfully entitled to remedy and where that remedy is disproportionately costly to the vendor (if it would cost them too much to repair) then you are entitled to replacement, or repair. You can rescind the contract if the vendor is not fulfilling their obligations. Good luck.

You might want to consider checking what Mazda's corrosion & perforation warranty covers in terms of timescales as it's usually longer than the standard 3 years mechanical.