haroon bhaiiiiiii.. how you doin mate??
yaar ali.. i think you should try one thing before you do that, get yourself local gaskit, desiiiiiii... fat one! that covers some of the leakage. if need put two gaskits. then see if the water reduces or not. and pay no labor to your mechanic since he didnt do it right the first time he should do it again.
once you do that, dont over stress your car since a local gaskit isnt that good. dont speed too much or speed with ac on. drive easy and it wont hurt. then if you reallllllllly want it alllll solved. then do what haroon said. but by doin that you'll have to change the engine number on your registration book.. big hastle.