Most of the listed seals are excellent American made reproductions of originals. The material is automotive grade "EPDM" rubber and will not deteriorate.
Deterioration is an occasional problem with "third world" seals. Where we are offering budget seals from third world countries we state this clearly in the product description.
When available we will list German origin seals.
Usually the German products are made in factories which use original VW dies or replicas. Reproductions tend to be excellent but rely on dies made from the part sample. This can result in more laborious installation (due to minor variations in detailing or in dimensioning.) However we have found that properly made reproductions are fully functional and easy to install.
Certain seals are interchangeable. For example the seals labelled #5 in certain cases. So we have used a "dot" or two after the part number where it is identical to another part. This way we can list the "same part numbers" as separate items.