The MZ or ZX series suffer often from a plastic mirror gear failure, but then the mirror flips to upward position ...
Loose is not typical unless a spring also broke... or another problem emerged.
If the gear error, If you are not afraid disassembling a camera, start here
MZ5n mirror blocked, service manual? - Page 2 - PentaxForums.com
The thread is long and evolved, but it contains what, how to repair and where spare gear can be obtained...
A search on this forum for ”MZ mirror gear” yields more results...
But MZ or ZX ’s (the name variant depends on Europe, America,... origin) are found cheap if you want an easy replacement....