Originally Posted By: old1
I never saw OIL on/in a foam filter dry out, as oil doesn't evaporate.
Filter oil has a solvent in it to allow it to spread through the foam, this then evaporates leaving the thicker tackier filter oil. I always try to use a filter oil for motorcycle foam filters, for lawnmowers it's too thick, and engine oil works best. I have used NoToil, but in my real world, I clean up messy filter changes in the parts washer, and that doesn't work with NoToil, you have to use some water based cleaner.