Replicating The Jet Washing Mode In Farm Simulator

Hi,

I am looking for some advice for a prototype/concept!

I want to replicate the jet washing mode of Farm Simulator, the tractor and trailers get dirty and you can park them up and spray them with the jet wash until they sparkle:



How do i go about this?

I can import a model from blender and using parenting i have a hierarchy allowing me to add a different material (in unity) to each part of the tractor (main body, doors, wheels, windows etc), but how do i go about adding a dirty texture that can then be cleaned based on a ray cast from a jet wash?

I was thinking that i can add a dirty texture somehow that can have it's opacity turned down based on a raycast while using the jet wash or is there a better way?

What options do i have to create the dirty textures, do i paint in blender, do i UV unwrap, can this be imported into unity, and how can i go about applying them to the model and then cleaning them?

if someone can point me the right direction with regards to what to look into it would be appreciated and any advice would be great!

Thanks