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I found out the information in the list below, other members may clarify whether this is correct. You might be better off buying a sump plug with integrated washer like the one from Supercheap in the link below, they look like they would never leak:
Holden Commodore VN, VP, VQ, VR (03/89-04/95), VS (with 12mm plug) 12mm-1.75 F-107 [V6 I would guess]
Holden Commodore VS (with 25mm plug) 25mm-1.5 FG-5 [V8 I would guess]
Holden Commodore VT V6 (with 14mm plug), VT V8 14mm-1.5 F-106
Holden Commodore VT V6 (with 24mm plug), VX, VX2, VY, Statesman WK, WH (3.8L V6) 24mm-1.5 FG-8
Holden Commodore VX V8, VY V8, VE V6 3.6L 12mm-1.75 F-107
http://www.supercheapauto.com.au/Product/Smart-O-Sump-Drain-Plug-M12-x-1-75mm-F1/341736