need tipps for retexturing

[OfenBrot]

Hey im currently working on some retexturing for some cars in a game and they have mud on it so here is my problem the mud is currently to pixelated and if i use a brush or something it looks like a censor how can i improve this so it looks like real mud ? (see attachments)

[PixLab]

mud... a proper mud is not easy to paint and the light on it can be a nightmare and there are so many type of muds...

Because I'm not good to paint, I would use a free photo stock from one of those website like pixabay or unsplash and so

On a new layer above the one on your OP, then a mask to keep only the part you'll like, and blend it overlay, screen/multiply but the blending mode will entirely depends of the photo, so try them all and play with opacity on each mode