Try this. Get some of the viscous epoxy penetrating liquid from Rotdoctor.com. $30. It will soak into the wood, nullifying the rot. Rebuild the balance of the rotted oar material with epoxy/microspheres putty mixture, then reshape. Finally, coat the blades with some fiberglass and wet it out. It may not look pretty, but it should hold together. Might cost you about $60. I may have some spare fiberglass cloth if you need enough to do two oars.