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They crack heads between the valve seats - its very common
mate $1200 to replace a motor (second hand) is way to high.. i say your getting ripped off because $690 for a second hand ecotec is a bit high.. wish i had of seen it early i could of changed your motor for like half that price. does heaps of ecotec replacements.. im even currently converting my vr from buick into manual ecotec..
$690 may be a bit high for the engine - but you don't know the circumstances - the mechanic might have two lots of freight on top of that (they sometimes want the old motor back) & prices go up & down with demand & availability -.