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
I stuck a tooth pick in the hole and it did not squirt fluid out ,,and the brakes worked . does that plug have a valve in it that I cannot see that lets air in as I pump the brakes and then lets air out too? Thinking that I need a new plug ?
