What are you scrubbing with? I use Simple Green and like the results. It does take several applications in the really cruddy areas. If there is a build up of grease/oil/dirt anywhere I start by trying to remove as much of that before I get started on the whole compartment. Sometimes this requires careful scraping and a modest amount of heavier duty solvent spray first.

I then spray the entire compartment with Simple Green (including the underside of the hood)and wash it with a wet sponge the first time. I rinse with a low pressure hose. After things dry I go back and spray the areas that are still dirty. A parts brush or a paint brush makes a good scrubbing tool. These areas are then washed and rinsed. Allow to dry again and go back and look for the areas that are still not clean and go through the procedure again. Once you have the compartment clean and dry you can spray it with Armoral (or similiar product of your choice). The Armoral will give you the "eBay look", but it doesn't last very long and may in fact accelerate future buildup.

If you are really anal you can wax the underside of the hood and the inner fenders after cleaning to make it easier to clean the next time.

Randy