Justsambam08 - mink oil is not really used in europe, I am told by others in the US that it is more of a grease than an oil, it's just called mink oil. As a grease rather than an oil it is OK to use on all your leatherwork.
Upnover - mineral oil is used by the tanners and curriers as part of the process to prepare the leather prior to dyeing and as such is not really bad for the leather, it is just the ammount used that is bad. After the dyeing process the curriers use ' curriers grease ' this is a combination of tallow ( rendered cow fat ), mineral or neatsfoot oil , cod liver oil and in somecases beeswax, the tallow makes up at least 75% of the mix so what you end up with is a grease - different curriers use a different that they over time have developed.
I will try to put it in terms that may make some sense - when you wash your car you don't take it to the local pool and submerge it, you use a bucket and sponge.
Natural oils are present in the cow hide , but the major part of the nourisment in the skin is a grease based substance , so what is recommended is to replace the grease to keep your leather in good condition.