When I mirror brushes to save work, it appears that it doesn't work properly and produces invalid brushes that don't load in vmf's or game
Generally, be very wary of mirroring things. The problem with the traditional Mirror Tool in Max is that is makes a negatively scaled version of the model. You can see this if you select the object and enter this into the MAXScript listener:
$.scale
You'll get a value of [-1,-1,-1]
The fix for this is to Reset XForm on it.
If you need to use Mirror, use the Mirror Modifier instead of the Transformation Mirroring.
ok thanks for the advice