It's a vent, which must be there if the brakes are going to work correctly. If fluid is squirting out of that hole, the reservoir is either overfilled or there's a failure of one of the MC piston seals.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!