Elastomers and Bio-Degradable Hydraulic Oil- The environmental benefits of using zinc-free and/or other types of bio-oil are significant. There are some “no-sheen” products out there which are especially attractive for use when working in sensitive areas.
Just a word of caution when selecting which oil might be best for your situation…Check the chemical compatibility of the elastomers in your O-rings and seal components; some of these bio-oils can aggressively attack certain types of seal and O-ring materials.