Do you know if they have been rebuilt/replaced since you've owned the vehicle or are they original equipment? If they have been rebuilt they may have a more modern type of oil. If they are original they will still have some form of glycerin based oil. The two don't mix. Penrite No. 2 shock oil is recommended for Houdaille type shocks used on Ford product if they have more modern wing shaft seal material incorporated. The old leather can only take glycerin.
Kerby