As a note on antique leather care I would like to mention a product I use on Imperial German leather goods. It's a British product I orginally found at a Jaguar dealer's parts shop. Hide Food is the trade name and it can be purchased through the internet.
Unlike Pecards and other such leather care products Hide Food contains no chemicals or petroleum based products. It will not darken linen stitching or leather if applied sparingly. On a pickelhaube, I would not hesitate to use it on the liner or draw string. It would not be appropriate for the exterior.