Hello Ishu,
The tension discs just do not wear out, they are supposed to be loose when the presser foot is up, new discs or tension unit won't solve a tension problem, when the tension is set about number 5 you should be able to sew very well, if the stitches are not coming out right then you will need to adjust the tension, you can adjust it further by pushing the numberered ring in and then turning the chrome screw clockwise bit by bit until you get it right.
drivewithken@blueyonder.co.uk, August 2008