for the new law-ie used cars from a trader
you must be able to prove that the fault was there when you purchased the vehicle-it is the customers obligation to prove this

in the case above i would try and negotiate a cash settlement and arrange repair elsewhere-on the mk2 golfs when they were new there was a buzzer that sounded when it lost oil pressure-the mk2 gti were bad for choking up the oil pick up[maybe lack of/poorer oil in the mid 80s],the clip on plastick windage pipe used to harden and fall off too