Check to see if your Grimlock's other features matches that of the mentioned Japanese variations in 'The Real Dinobots!' section of the variations site.

Type 1: smooth head, no locktab on chest (Japan)
Type 2: tabbed head, tabbed-chestpieces (Japan)
Type 3: tabbed head, tabbed-chestpieces (Macau)
Type 4: Gen-2; silver, turquoise, or blue (china)