My two cents worth – Defer to a conservator’s recommendation if this is an artifact in the permanent collection. Their input on how much restoration/repair or replacement is warranted for the integrity of the piece will be your guiding advice.
However, if this is a hands on use or educational piece I would say that if the “bones” are sound I would advocate for replacing only those elements too far gone to maintain integrity and functionality. Take lots of photos of the process and fully document the materials, how they are attached to the original elements and all suppliers.
Curator of Collections
Lakeshore Museum Center