Are you lubing the springs themselves or the bushings at their ends? If you've got creaking noises, that's most likely where it's coming from. Replacing the bushings is likely what you need to do.
If it's the bushings making noise, rubber is not compatible with petroleum products, FYI. Polyurethane bushings are especially prone to squeaks, and they are really not compatible with petroleum products, either. A silicone based grease like Sil-Glyde would be what I would use in either case if I were trying to lubricate them