Thats not the breathing hole . Breather is at the oilfiller cap at the back with the fillercap.
If you remove the gearshifterover and look at the ack of that shiftercover you will see all the ports for the IPTO clutch/ brake and the MFWD and if equepped the hi-low. I think 4 bolts with different lenthes hold that "sandwitch" together. Check that the correct bolt is at the correct hole AND that those gaskets is not blowen ?