manual transmission drain plug

Next to the transmission drain plug, about 2 inches to the left there is a small hole does this serve as a breather hole or an overflow for the fluid. Also on the top of the transmission, once you disconnect the actual shifter, there are four small bolts that hold the bottom end of the shifter, below that there is a spacer (an extension of the transmission )of some kind and then there are another 4 bolts that actually mount that piece to the transmission and below that a gasket I want to replace. which set of bolts do I loosen to be able to replace the gasket. any suggestions, thanks.