Is this going to end up on a diorama, M1??? If so, instead of using paint to replicate mud, get yourself some Paris plaster, mix it with a bit of water and some earth brown acrylic paint, then slap the mixture onto your model's tracks and wheels, adding yet more onto the fenders, the front and back of the hull, the engine deck (where troops would congregate!). I would use this to disguise the place where the tracks are joined together. In very muddy conditions, there wouldn't be much of the camouflage left to see on the wheels, the bottom and sides of the hull. And the tracks themselves would be covered in it too.