Yeah, that seems to be what's happening to our overhead springs... getting pretty darn rusty after only being open just over one year...I would not recommend lithium grease, at least not the stuff in a spray can. D&S used to recommend using it on the 5000's arch chains, but it absorbed water and made the chain rust. Somewhere on an old phone I have pictures of chain I removed that was rusted solid into a stick of steel. Later on they said use only bar and chain oil.
Do you have a link for them please? Definitely worth looking into.You can purchase HDG and stainless torsion springs if corrosion is an issue. All of ours are HDG and I have had no corrosion after 10 plus years.
It's mineral oil/kerosene/paraffin oils and "proprietary ingredients."BTW, WD-40 is water based and dries out