After replacing the three failing HDDs in the Gannet (Synology) expansion unit, I contacted the company (Maestro Technology LLC) via Amazon. They have been very responsive and very helpful, with no resistance whatsoever. They indicated the drives were new when I ordered them and they seemed surprised that the warranties for all three had already expired.
Regardless, they simply said they’ll replace the threee drives once they receive these three failing HDDs. They provided a return shipping lable for FedEx, so I packaged up the HDDs and sent them back. Hopefully we’ll hear back soon.