The maintenance manual will state specific limits for allowable oil consumption. this figure is usuall quoted as quarts or pints per hour. If it is a repeat write up the are obliged to sign off the defect as in limts per amm 7x-xx-xx. Do not accept a sign off as eng run carried out no leaks evident. Ask to see a copy of the mm and work out the oil consumption per flt hour from the uplifts in the tech log. Irregardless if it is in limits or not, you are within your rights to refuse an aircraft, especially for a defet such as this. Oil leaks never get better. hope this helps