I don't think your missing much sounds like you have figured it out.
older fleet / high hours and the usual operators who don't either care or have not been educated lol.

If MIL lamp for low brushes is working correctly on the units then the employees are not doing their job reporting defects or as you said locking them out. This is entirely out of your hands. Management has a responsibility to identify high cost areas of maintenance within its operation and take action amending procedures or disciplining operators and holding employees accountable who don't follow them resulting in equipment damage.