have a look at the "detailed identification" at the top of the page, id say it is because of the lower gvm and seat cap but i could be wrong, check out the identification section, ive got it printed out and im my car and check anything i see, [MENTION=225]HK1837[/MENTION] would be able to say for sure

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http://mysandman.com.au/ident.html
the trims 18v? it says hx sandman had 18v