If you’re planning on repairing that Moen, I would probably drill out the set screw, remove the trim and replace the faucet. 16 years has been quite a long service life for a shower valve.
Sixteen years is not a long time in the service life of a good shower valve, and Moen valves are fairly good.
Many of them can last fifty years easily.
Now, it might be time for a new valve cartridge.