"essentially wool grease (whatever that is) "----Kestas

Wool Grease is Lanolin. This is used in hand lotions and many leather care products to put back into the skin the oils being lost to ( whatever, including air ) to keep the leather from drying out. For leather there is no turning back from the effects of drying out. It can be halted or slowed... but any damage from the drying and breaking of the interconnecting fibers which give leather its combination of strength and feel can not be repaired.

This use of lanolin for rust prevention has also been discussed under the name of some kind of ' film'... my Ford Tractor dealer carries it in spray and brush on... and it typically lasts several years in non washed areas... . and is thin enough not to need further thinning...

which brings up another point.... if you use something like mineral spirits to thin a product so it can be sprayed.... one would want to test it first (unless the manufacturer lists it as a suitable thinner) because some thinning agents might prevent the crosslinking and long chain formation common to the products means of becoming strong and long lasting....