Ellen,
As a conservator who has examined and treated dozens of sleighs, I have never seen runners such as the ones you show. Could you explain a little more about them? The wooden portions are huge by normal sleigh standards and the iron runners are extremely thin but unusually wide. Are these folk-made runners for some other purpose?
It appears in the photo that there is some fungal decay of the wood. Is the wood painted? Are there any exit holes from powder post beetles or other insects? If you have not done it already, I would start by HEPA vacuuming them. This would remove dirt and mold that may be present. Be careful around the fungally-decayed areas.
If you can provide any more information, I may be able to give you some more specific advice. Also helpful would be higher-resolution photos. If the limitation is this forum, feel free to email them directly to me at acc@conservator.com.
Marc