This is very common in Lemanias....especially the last series silverstone.
the movement is held down with the retaining ring and then the zigzag spring ring ontop.
the caseback then screws down ontop squeezing them.
make sure the caseback thread is really clean first. add some angles to the zigzag spring as this can flaten. If your missing the spring try using thick rubber or nylon gaskets.
good luck