Jean-Guy.
Rust Check also softens rubber (but they deny it). I don't know about Krown.
I have used chain saw oil (winter weight) mixed with kerosene (to thin it) but have not found any anti-rust additive (yet). I'm planning on buying a 4L bottle from Krown for this winters application.
-Larry (Ontario, Canada)

Jean-Guy Savoie wrote:

A number of references on the net speak of using MOTOR OIL for rust proofing. DON'T DO IT. Aside from the stink, it will rot rubber (hoses, insulating pads, grommets, Door seals etc...) and some plastics. The conventional wisdom, here, is that transmission oil will not rot the rubber, but there is some smell and I suspect that the transmission oil might melt or disolve the OEM wax because it is so "detergent", but I don't know this for sure. Does anyone know any more about the subject?