Hi Linday, its very unlikely that a core plug needs replacing, ignoring the rusty plugs for now it sounds like the diagnostics indicated the coil pack which is a very common failing on these engines about £40 very easy to fit four mounting bolts one electrical connector and the four HT plug leads, the rusty spark plugs they might of been in there since new unless you know the service history, if a core plug was leaking you would have to be constantly topping up the radiator expansion tank and you might well be constantly overheating.
nigel
May 2008
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