Yes, the colours have to be solid for the masking to work as it should. So padding or diffusion on a single island like this leads to errors as the texture bleeds onto itself.
Try to tone down the scratches in the diffuse and ramp them up with some contrast in the spec/gloss. I think you will be much happier with the results in the render.
PBR textures should have no lighting information (With the exception of Ambient Occlusion). This is unlike the old system where Ambient Occlusion would be put into the diffuse map.