High power pressure washer, and loads of time.
Give everything a good blast, let it soak for a few minutes, then blast again. Repeat as needed.
If it's 2 pieces of metal that are seized togeter with salt, then break out the grinder.
When dealing with salt, water and patience are your friend. I used to have to clean 18 highway salt spreaders every spring, and this was the hot ticket for getting it out of the tight spots.
Try up-ending the assembly into a trash can full of water.