What solvent for parts washer?

Rusty wrote: "Also, on every parts washer I have ever seen.......at least since the 1980s they clearly say not to use petroleum based cleaners as that will hurt the pump."

I wonder if they say that because naptha will hurt the pump, or for liability reasons? In any event, I've been putting naptha through my pump for awhile now and it still works. I hope I am not speaking too soon.