Creality Ender3 Idler Pulley Nut Replacement

As many others before - I ran into issues after an almost finished print job of 14h. The timing belt skipped somehow. I found some issues on my Ender3 that need a fix before starting the job again.

X-Axis: Timing belt tension reduced, the Hot-End needed adjustment back to 90° and after detailed inspection the belt made some grinding noise on the right side.

After tighten the play at the mount plate, adjustment of the Hot-End itself I noticed that the M8 nut at the idler pulley seems to be