well, depending on how much you want to tear it down,
Engine degreaser
Simple green,
Brake Cleaner
Any of those will get crud off, I would get anything greasy or grease+dirt scraped off with a plastic puddy knife, then I'd start with simple green and a brush since it smells good, works pretty well and isn't going to make any problems for you with disposal.
A good brushing and hot water and you'll get most of it off.
Then i'd do a quick squirt of brake cleaner anywhere it is being more stubborn.