how to fix or replace bight control set singer 319k ?

I have recently aquired a singer 319k sewing machine, its the model with the decorative cams. I cleaned and serviced the machine but found that the machine would only sew with the needle set all the way to the left and i couldn't get it to zigzag. I had a look at the bight control set and found that when i moved the lever that controls the needle the mechanism inside didnt move but it does still move the needle left and right. I purchased a replacement but i cant remove the old one. Any help would be greatly appreciated rebecca