Hello Impasto On Board and welcome to the ArtRage forums 
It sort of sounds as if you may not have actually had your ‘Custom Brush 1’ preset selected before starting your adjustments?
To be sure you are selecting the correct Custom Brush for re-editing, my steps would be these;
Open the Brush Designer panel.
In the area top right of the panel it will say which brush preset has loaded. If it is not the preset you want to edit, click on this name and in the fly-out menu that opens find your Group/folder ‘Oil Brush’ and then select your brush 'Custom Brush 1' inside it.
Now make the changes that you want to the brush. Note, when you start making changes to the brush, where it's name was displayed will automatically change to saying 'Presets...'
When happy with your changes, click again in the top right area that now says 'Presets...', and in the fly-out menu choose 'New Preset' at the top.
Name your new brush and select (if needed) a Group/folder for it to live in. Or (if needed) click on the small menu icon top right of the 'New Presets' panel to create a new Group/folder for the preset to live in.
When done click the tick box bottom right of New Preset panel.
Now click OK to close the Brush Designer.
Hope some of all that was helpful but don't hesitate to ask if you have more questions
Maker Of Replica Macoys
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