Where is the gearbox oil level plug on a 2006 Mazda 3?

On a 2006 Mazda 3, the gearbox oil level plug is located on the side of the transmission case. To check the oil level, you typically need to remove the plug using a wrench or socket. The oil should be at the level of the plug hole; if it spills out when you remove the plug, the level is adequate. If no oil comes out, it may need to be topped up.