Don't use oil on any of your leather at any time - oil is bad for your leather as it weakens the fibrous structure.
Use a leather dressing - if in any doubt it should resemble fat or grease, if it is a liquid then don't use it. If you can get it Carr Day and Martin produce a dressing called Ko-cho-line which is good.
Clean your leather with saddle soap , then after it has dried apply the dressing ( warm it up, and put it on with your hands, not a cloth ( unless you have exema ), do this after you have ridden or at least 36 hours before.
Put a small ammount on the shiny ( grain ) side, but most on the flesh side. A can of Ko-cho-line should last about 6 months.