Should be on all 4L60E auto V6's from VT onwards (also 5L & Gen3 fitted with 4L60E trans). VS models had problems with people towing without sufficient cooling and there were some incidences where trans fluid was pushed up and out the trans dipstick tube and onto the exhaust manifold causing fires. Holden recalled that problem by fitting locking dipstick caps and insisting that a tow pack be fitted if the owners intention was to tow with the vehicle. From VT models onwards the locking dipstick cap and trans cooler came factory fitted.