Check with a dealer or parts store to see if there's a different part number for an ABS master cylinder. There is usually a return line to the reservoir for all four brakes on the ABS system, for when the solenoid valves vent fluid back to the M/C during ABS operation.
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!