I have to second that vote for simple green. It's a awesome product. Can be used for cleaning counter tops in the kitchen to a parts washer.
One think that I came to my mind was if you could heat you WATER base cleaner in the parts washer. From my experience hot cleaners will work better than cold. Maybe a block heater?? Just an Idea. And from their web site they recommend 1 cleaner to 1-20 parts water for a parts washer. http://www.simplegreen.com