Usually, WD40 is not a good choice for cleaning up a machine - it can dry and leave a residue. I would have started the clean up with some Dawn (diluted slightly) and then if needed graduate to something stronger. Maybe a bit of Goop on the bottom of that machine. Just because you find it on the curb or in the garbage doesn't mean you need to go all out and strip paint etc off a machine. It is good to have a machine you don't have a lot invested in to experiment with - ask me how I know. I would especially not use anything harsh on a machine with plastics (I know this one isn't but just for future reference - plastic can melt) Muv has some really good videos about cleaning up a machine. Most of the time it is all they really need.
http://www.quiltingboard.com/vintage...v-t167789.html Muv also makes marmalade
Ok I read where there is rust involved as well. You need some rust remover for that. Most people go overboard on the chemicals right from the start.