Hi Francisco:
Although the top portion of the different reel adapters are not alike, bottom round portion with three black plastic latch that are spring loaded are the same for all Studer Master Recorders.
The trick in re-assembling the adapter is to partially assemble the bottom plate onto the top portion leaving some space in between where the spring and the black plastic latch go into. As you hold the partially assembled adapter, you put in the small spring and follow it with the plastic piece one by one while keep paying attension to keeping the assembly together. After you have inserted both springs and the plastic latches, then you screw the bottom pieces in completely. Make sure you are not pinching the springs.
Try it, it will work. If you still can't get the assembly to go together, let me know. I will disassemble one and take photos of assembly steps for you.
Ki