I'm sure WD-40 would be MUCH more expensive, but I feel a little safer under a car with a can of WD-40. 
I noticed that too. Probably a good idea to dilute 50/50. I worked on restoring a 50's soda fountain and we used diluted Dawn dish-washing liquid and that worked well too.
I get a lot of strange looks when I state I used gas, especially when they see that I am a smoker!
Well, first, I never smoked when working with gas. I kept the garage bay door open, and the car was up on my lift. I used a metal oil drain pan, and poured a pint or so of gas into the pan, which was located outside of the garage. I then dipped a rag in the gas, took it inside, and went to work. When it became difficult to remove grime, that told me that the gas had evaporated from the rag. Back outside, dip, back inside, repeat over and over. I went through 3 or 4 five-pound bags of rags. A very safe process!
