Alright, 1.7.8 is letting me apply Grungit again.
I am encountering a weird issue though. When Grungit finishes baking I get the little 'Cancel" text in the top left corner and GPU rendering won’t work anymore. Checking in preferences, toggling the GPU off and on again briefly fixes it but moving in the view port breaks the GPU rendering again so saving and loading the project is the only way to actually fix it. Once you do that, it’s revealed the bake didn’t complete.
It’s interesting as well, the texture displays in Blender but doesn’t open in Photoshop (just locks PS up, as if it’s a corrupted file).