Kevin,
The Frisco 1522 crew used to use a strong solution of the Cleaner "Simple Green". The UP crew has used it in the past, also.
Its' environmentally friendly and since it can be purchased at a place like Sam's Club, you don't need to buy a 55 gallon drum to experiment with it to see how it works for you.
It's not like Oakite and won't take the paint off it that's what you're looking for.
I don't know where you'd find a solvent like that today. It seems that the California pollution legislation has pretty much affected the whole country.
Rick Steele